fix: use npm instead of pnpm in Dockerfile

pnpm-lock.yaml was out of date after Next.js upgrade, switched to npm ci
for more reliable builds.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Dockerfile

@@ -5,8 +5,8 @@ FROM base AS deps
 RUN apk add --no-cache libc6-compat
 WORKDIR /app
 
-COPY package.json pnpm-lock.yaml* ./
-RUN corepack enable pnpm && pnpm install --frozen-lockfile
+COPY package.json package-lock.json* ./
+RUN npm ci
 
 # Rebuild the source code only when needed
 FROM base AS builder
@@ -17,7 +17,7 @@ COPY . .
 ENV NEXT_TELEMETRY_DISABLED=1
 ENV NODE_ENV=production
 
-RUN corepack enable pnpm && pnpm run build
+RUN npm run build
 
 # Production image, copy all the files and run next
 FROM base AS runner