fix(timezone): all date/time display now uses IST (Asia/Kolkata)

New src/lib/date-ist.ts utility:
- hourIST()   — current hour in IST (replaces new Date().getHours() on server)
- isTodayIST() / dateIST() — IST-aware "today" comparisons
- fmtTime()   — time display with timeZone: "Asia/Kolkata"
- fmtDate()   — date display with timeZone: "Asia/Kolkata"
- dayLabel()  — "Today" / "Yesterday" / "Mon, 26 May" in IST

Applied across: home (greeting, today-summary, log times),
activity (day grouping, bar chart, log times), ai, growth,
milestones, settings — eliminating Finland-timezone artifacts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/(app)/activity/page.tsx

@@ -8,6 +8,7 @@ import { api } from "@/lib/api";
 import { CalendarView } from "@/components/CalendarView";
 import { LogModal, type LogType as ModalLogType, type SmartDefault } from "@/components/LogModal";
 import type { Log, LogType } from "@/types";
+import { dateIST, todayIST, fmtTime, fmtDate, dayLabel } from "@/lib/date-ist";
 
 type ViewMode = "timeline" | "calendar";
 
@@ -23,13 +24,9 @@ function getIcon(type: LogType) {
   return "📝";
 }
 
+// dateStr is now an IST YYYY-MM-DD string (from dateIST())
 function formatDayLabel(dateStr: string): string {
-  const d         = new Date(dateStr);
+  return dayLabel(dateStr);
-  const today     = new Date().toDateString();
-  const yesterday = new Date(Date.now() - 86_400_000).toDateString();
-  if (d.toDateString() === today)     return "Today";
-  if (d.toDateString() === yesterday) return "Yesterday";
-  return d.toLocaleDateString("en-IN", { weekday: "short", month: "short", day: "numeric" });
 }
 
 export default function ActivityPage() {
@@ -100,8 +97,8 @@ export default function ActivityPage() {
   };
 
   // Today's stats (computed from loaded logs — no extra fetch)
-  const todayStr    = new Date().toDateString();
+  const todayStr    = todayIST();
-  const todayLogs   = logs.filter(l => new Date(l.loggedAt).toDateString() === todayStr);
+  const todayLogs   = logs.filter(l => dateIST(l.loggedAt) === todayStr);
   const todayCounts = {
     feed:   todayLogs.filter(l => l.type === "feed").length,
     sleep:  todayLogs.filter(l => l.type === "sleep").length,
@@ -111,21 +108,21 @@ export default function ActivityPage() {
   // Last 4 calendar days (computed from loaded logs — no extra fetch)
   const last4Days = Array.from({ length: 4 }, (_, i) => {
     const d       = new Date(Date.now() - i * 86_400_000);
-    const dateStr = d.toDateString();
+    const dateStr = dateIST(d);
-    const dayLogs = logs.filter(l => new Date(l.loggedAt).toDateString() === dateStr);
+    const dLogs   = logs.filter(l => dateIST(l.loggedAt) === dateStr);
     return {
       date:   dateStr,
-      label:  i === 0 ? "Today" : i === 1 ? "Yest." : d.toLocaleDateString("en-IN", { weekday: "short" }),
+      label:  i === 0 ? "Today" : i === 1 ? "Yest." : fmtDate(d, { weekday: "short" }),
-      feed:   dayLogs.filter(l => l.type === "feed").length,
+      feed:   dLogs.filter(l => l.type === "feed").length,
-      sleep:  dayLogs.filter(l => l.type === "sleep").length,
+      sleep:  dLogs.filter(l => l.type === "sleep").length,
-      diaper: dayLogs.filter(l => l.type === "diaper").length,
+      diaper: dLogs.filter(l => l.type === "diaper").length,
     };
   });
 
   const filteredLogs = filter === "all" ? logs : logs.filter(l => l.type === filter);
 
   const groupedByDay = filteredLogs.reduce<DayLogs[]>((acc, log) => {
-    const date     = new Date(log.loggedAt).toDateString();
+    const date     = dateIST(log.loggedAt);
     const existing = acc.find(d => d.date === date);
     if (existing) existing.logs.push(log);
     else          acc.push({ date, logs: [log] });
@@ -359,7 +356,7 @@ export default function ActivityPage() {
                           </div>
                           <div className="flex items-center gap-1.5 flex-shrink-0">
                             <span className="text-sm text-gray-400">
-                              {new Date(log.loggedAt).toLocaleTimeString([], { hour: "2-digit", minute: "2-digit" })}
+                              {fmtTime(log.loggedAt)}
                             </span>
                             <span className="text-gray-300 dark:text-gray-600 group-hover:text-rose-400 transition-colors text-base leading-none">›</span>
                           </div>
@@ -413,7 +410,7 @@ export default function ActivityPage() {
                   {[
                     selectedLog.subType?.replace(/_/g, " "),
                     selectedLog.amount ? `${selectedLog.amount}ml` : null,
-                    new Date(selectedLog.loggedAt).toLocaleTimeString([], { hour: "2-digit", minute: "2-digit" }),
+                    fmtTime(selectedLog.loggedAt),
                   ].filter(Boolean).join(" · ")}
                 </div>
               </div>
@@ -473,7 +470,7 @@ export default function ActivityPage() {
         const { date: sheetDateStr, type: sheetType } = daySheetDate;
         const sheetLogs = logs
           .filter(l =>
-            new Date(l.loggedAt).toDateString() === sheetDateStr &&
+            dateIST(l.loggedAt) === sheetDateStr &&
             l.type === sheetType
           )
           .sort((a, b) => new Date(b.loggedAt).getTime() - new Date(a.loggedAt).getTime());
@@ -538,7 +535,7 @@ export default function ActivityPage() {
                       </div>
                       <div className="flex items-center gap-2 flex-shrink-0">
                         <span className="text-sm text-gray-400">
-                          {new Date(log.loggedAt).toLocaleTimeString([], { hour: "2-digit", minute: "2-digit" })}
+                          {fmtTime(log.loggedAt)}
                         </span>
                         <span className="text-gray-300 dark:text-gray-600 group-hover:text-rose-400 transition-colors text-lg">›</span>
                       </div>

src/app/(app)/ai/page.tsx

@@ -4,6 +4,7 @@ import { useState, useEffect } from "react";
 import { useFamily } from "@/app/FamilyProvider";
 import { Button, Input, ConfirmDialog } from "@/components/ui";
 import type { AIChat, ChatSession } from "@/types";
+import { fmtDate } from "@/lib/date-ist";
 
 export default function AIChatPage() {
   const { childId } = useFamily();
@@ -186,7 +187,7 @@ export default function AIChatPage() {
               >
                 <div className="flex-1 min-w-0">
                   <div className="text-sm font-medium truncate dark:text-gray-100">{session.title}</div>
-                  <div className="text-xs text-gray-400 dark:text-gray-500">{new Date(session.updatedAt).toLocaleDateString()}</div>
+                  <div className="text-xs text-gray-400 dark:text-gray-500">{fmtDate(session.updatedAt)}</div>
                 </div>
                 <button
                   onClick={(e) => { e.stopPropagation(); setDeleteConfirm(session.id); }}

src/app/(app)/growth/page.tsx

@@ -6,6 +6,7 @@ import { useFamily } from "@/app/FamilyProvider";
 import { Button, Card, Input, ConfirmDialog } from "@/components/ui";
 import { WHO_BOY_WEIGHT, WHO_GIRL_WEIGHT, getAgeInMonthsFromBirth, getPercentile } from "@/lib/growth-standards";
 import { formatAge } from "@/lib/formatting";
+import { fmtDate } from "@/lib/date-ist";
 import type { GrowthRecord, Goal } from "@/types";
 import {
   Chart as ChartJS,
@@ -190,7 +191,7 @@ export default function GrowthPage() {
 
     const headers = ["Date", "Weight (kg)", "Height (cm)", "Head (cm)", "Notes"];
     const rows = growthData.map(r => [
-      new Date(r.measured_at).toLocaleDateString(),
+      fmtDate(r.measured_at),
       r.weight_kg || "",
       r.height_cm || "",
       r.head_circumference_cm || "",
@@ -423,7 +424,7 @@ export default function GrowthPage() {
             <div>
               <div className="font-semibold text-rose-600 dark:text-rose-300">Latest Reading</div>
               <div className="text-sm text-gray-500">
-                {new Date(latest.measured_at).toLocaleDateString()} ({child ? formatAge(child.birthDate, latest.measured_at) : ""})
+                {fmtDate(latest.measured_at)} ({child ? formatAge(child.birthDate, latest.measured_at) : ""})
               </div>
             </div>
             {velocity && (
@@ -637,7 +638,7 @@ export default function GrowthPage() {
                 <div key={i} className="p-3 bg-gray-50 dark:bg-gray-700 rounded-lg hover:shadow-md transition-shadow flex justify-between items-center">
                   <div>
                     <div className="text-sm text-gray-500">
-                      {new Date(record.measured_at).toLocaleDateString()} ({child ? formatAge(child.birthDate, record.measured_at) : ""})
+                      {fmtDate(record.measured_at)} ({child ? formatAge(child.birthDate, record.measured_at) : ""})
                     </div>
                     <div className="flex gap-2 mt-1">
                       {record.weight_kg && (

src/app/(app)/home/page.tsx

@@ -8,6 +8,7 @@ import { useStageCheck, type BabyStage } from "@/hooks/useStageCheck";
 import { LogModal, type LogType } from "@/components/LogModal";
 import { getOfflineQueue, processOfflineQueue } from "@/lib/offline-queue";
 import { calculateAge, formatTimeAgo } from "@/lib/formatting";
+import { hourIST, isTodayIST, fmtTime } from "@/lib/date-ist";
 import type { Log, AIChat, ChatSession } from "@/types";
 
 async function getSessions(cid: string): Promise<ChatSession[]> {
@@ -32,15 +33,14 @@ async function createSession(cid: string): Promise<ChatSession | null> {
 
 
 function getGreeting() {
-  const hour = new Date().getHours();
+  const hour = hourIST();
   if (hour < 12) return "Good morning";
   if (hour < 18) return "Good afternoon";
   return "Good evening";
 }
 
 function TodaySummary({ logs }: { logs: Log[] }) {
-  const todayStr = new Date().toDateString();
+  const today = logs.filter(l => isTodayIST(l.loggedAt));
-  const today    = logs.filter(l => new Date(l.loggedAt).toDateString() === todayStr);
   const counts   = {
     feed:   today.filter(l => l.type === "feed").length,
     diaper: today.filter(l => l.type === "diaper").length,
@@ -400,7 +400,7 @@ export default function HomePage() {
       <TodaySummary logs={recentLogs} />
 
       {stage && (() => {
-        const h = new Date().getHours();
+        const h = hourIST();
         type Suggestion = { label: string; type: "feed" | "sleep" | "diaper" };
         const matrix: Record<BabyStage, Suggestion> =
           h >= 5  && h < 9  ? { newborn: { label: "Feed", type: "feed" }, infant: { label: "Feed", type: "feed" }, sitter: { label: "Feed", type: "feed" }, crawler: { label: "Feed", type: "feed" }, toddler: { label: "Feed", type: "feed" }, walker: { label: "Feed", type: "feed" } } :
@@ -465,7 +465,7 @@ export default function HomePage() {
             <div key={log.id} className="flex items-center justify-between p-3 bg-white dark:bg-gray-800 rounded-xl">
               <div className="flex items-center gap-3">
                 <span className="text-xl">{log.type === "feed" && "🍼"}{log.type === "sleep" && "😴"}{log.type === "diaper" && "🚼"}</span>
-                <div><div className="font-medium capitalize">{log.type}</div><div className="text-xs text-gray-500 dark:text-gray-400">{new Date(log.loggedAt).toLocaleTimeString([], { hour: "2-digit", minute: "2-digit" })}</div></div>
+                <div><div className="font-medium capitalize">{log.type}</div><div className="text-xs text-gray-500 dark:text-gray-400">{fmtTime(log.loggedAt)}</div></div>
               </div>
               {log.amount && <span className="text-sm text-gray-500 dark:text-gray-400">{log.amount}ml</span>}
             </div>

src/app/(app)/milestones/page.tsx

@@ -4,6 +4,7 @@ import { useFamily } from "@/app/FamilyProvider";
 import { useStageCheck } from "@/hooks/useStageCheck";
 import { MILESTONES, type MilestoneDef } from "@/lib/milestones";
 import { Button, Input } from "@/components/ui";
+import { fmtDate } from "@/lib/date-ist";
 
 type Category = "all" | "social" | "motor" | "language" | "cognitive";
 type Filter = "all" | "achieved" | "upcoming";
@@ -194,7 +195,7 @@ export default function MilestonesPage() {
                   <p className="text-xs text-gray-400 mt-1">{m.ageRangeLabel}</p>
                   {m.achieved && m.achievedAt && (
                     <p className="text-xs text-green-600 dark:text-green-400 mt-1">
-                      {new Date(m.achievedAt).toLocaleDateString("en-IN", { day: "numeric", month: "short" })}
+                      {fmtDate(m.achievedAt, { day: "numeric", month: "short" })}
                     </p>
                   )}
                   <span className={`inline-block text-xs px-1.5 py-0.5 rounded-full mt-2 ${CATEGORY_COLORS[m.category]}`}>

src/app/(app)/settings/page.tsx

@@ -7,6 +7,7 @@ import { useTheme } from "@/app/ThemeProvider";
 import { useFamily } from "@/app/FamilyProvider";
 import { Button, Card, Input, Select, Badge } from "@/components/ui";
 import { StorageMeter, MemberLimitBanner } from "@/components/StorageMeter";
+import { fmtDate } from "@/lib/date-ist";
 
 interface Member {
   id: string;
@@ -81,7 +82,7 @@ export default function SettingsPage() {
       if (records.length === 0) { alert("No growth records to export."); return; }
       const headers = ["Date", "Weight (kg)", "Height (cm)", "Head (cm)", "Notes"];
       const rows = records.map((r: { measured_at: string; weight_kg: number | null; height_cm: number | null; head_circumference_cm: number | null; notes: string | null }) => [
-        new Date(r.measured_at).toLocaleDateString(),
+        fmtDate(r.measured_at),
         r.weight_kg ?? "",
         r.height_cm ?? "",
         r.head_circumference_cm ?? "",
@@ -315,7 +316,7 @@ export default function SettingsPage() {
                     <div key={invite.id} className="flex justify-between items-center p-2 bg-gray-50 dark:bg-gray-700 rounded text-sm mb-1">
                       <div>
                         <div className="font-medium text-gray-800 dark:text-gray-100">{invite.email}</div>
-                        <div className="text-xs text-gray-400">Pending · expires {new Date(invite.expiresAt).toLocaleDateString()}</div>
+                        <div className="text-xs text-gray-400">Pending · expires {fmtDate(invite.expiresAt)}</div>
                       </div>
                       <button
                         onClick={() => deleteInvite(invite.id)}

src/lib/date-ist.ts

@@ -0,0 +1,86 @@
+/**
+ * date-ist.ts — IST-aware date/time helpers.
+ *
+ * All functions explicitly pass timeZone: "Asia/Kolkata" so they produce
+ * consistent IST output regardless of where they run — Next.js SSR on a
+ * European server OR the user's browser.
+ *
+ * Never use new Date().toDateString(), .getHours(), or .toLocaleString()
+ * without a timeZone option — those use the host's local timezone.
+ */
+
+const TZ = "Asia/Kolkata";
+const LOCALE = "en-IN";
+
+/** ISO date string (YYYY-MM-DD) for today in IST — use for comparisons. */
+export function todayIST(): string {
+  // "sv-SE" locale gives YYYY-MM-DD — a clean, comparable format.
+  return new Date().toLocaleDateString("sv-SE", { timeZone: TZ });
+}
+
+/** ISO date string (YYYY-MM-DD) for any timestamp, evaluated in IST. */
+export function dateIST(isoOrDate: string | Date): string {
+  return new Date(isoOrDate).toLocaleDateString("sv-SE", { timeZone: TZ });
+}
+
+/** True if the given timestamp falls on today in IST. */
+export function isTodayIST(isoOrDate: string | Date): boolean {
+  return dateIST(isoOrDate) === todayIST();
+}
+
+/** ISO date string N calendar days before today in IST. */
+function nDaysAgoIST(n: number): string {
+  const d = new Date();
+  d.setDate(d.getDate() - n);
+  return d.toLocaleDateString("sv-SE", { timeZone: TZ });
+}
+
+/** Current hour 0-23 in IST. Replaces new Date().getHours() on the server. */
+export function hourIST(): number {
+  // Intl gives a locale-formatted hour string; parseInt handles "24" edge case.
+  const str = new Intl.DateTimeFormat(LOCALE, {
+    timeZone: TZ,
+    hour: "numeric",
+    hour12: false,
+  }).format(new Date());
+  const h = parseInt(str, 10);
+  return h === 24 ? 0 : h;
+}
+
+/** Format a timestamp as "hh:mm AM/PM" in IST. */
+export function fmtTime(isoOrDate: string | Date): string {
+  return new Date(isoOrDate).toLocaleTimeString(LOCALE, {
+    timeZone: TZ,
+    hour: "2-digit",
+    minute: "2-digit",
+  });
+}
+
+/** Format a timestamp as a date string in IST with given Intl options. */
+export function fmtDate(
+  isoOrDate: string | Date,
+  opts: Intl.DateTimeFormatOptions = { day: "numeric", month: "short", year: "numeric" }
+): string {
+  return new Date(isoOrDate).toLocaleDateString(LOCALE, { timeZone: TZ, ...opts });
+}
+
+/**
+ * "Today" | "Yesterday" | "Mon, 26 May" — for activity group headers.
+ * Replaces the toDateString()-based pattern throughout the app.
+ */
+export function dayLabel(isoOrDate: string | Date): string {
+  const d = dateIST(isoOrDate);
+  if (d === todayIST())       return "Today";
+  if (d === nDaysAgoIST(1))   return "Yesterday";
+  return fmtDate(isoOrDate, { weekday: "short", month: "short", day: "numeric" });
+}
+
+/**
+ * Like dayLabel but short ("Today" | "Yest." | "Mon").
+ * Used in the activity page bar chart labels.
+ */
+export function shortDayLabel(isoOrDate: string | Date, index: number): string {
+  if (index === 0) return "Today";
+  if (index === 1) return "Yest.";
+  return fmtDate(isoOrDate, { weekday: "short" });
+}