Dockerfile: use pnpm instead of npm

- Replace npm ci with pnpm install --frozen-lockfile
- Use corepack to enable pnpm
- Update COPY for pnpm-lock.yaml

Dockerfile

@@ -2,8 +2,8 @@
 FROM node:22-alpine AS deps
 RUN apk add --no-cache libc6-compat
 WORKDIR /app
-COPY package.json package-lock.json ./
-RUN npm ci
+COPY package.json pnpm-lock.yaml ./
+RUN corepack enable pnpm && pnpm install --frozen-lockfile
 
 # Stage 2: Build the app
 FROM node:22-alpine AS builder
@@ -11,7 +11,7 @@ RUN apk add --no-cache libc6-compat openssl
 WORKDIR /app
 COPY --from=deps /app/node_modules ./node_modules
 COPY . .
-RUN npm run build
+RUN corepack enable pnpm && pnpm run build
 
 # Stage 3: Production runner
 FROM node:22-alpine AS runner