hoàn thành bước tạo docker compose

frontend/Dockerfile

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+# ── Stage 1: deps ─────────────────────────────────────────────────────────────
+FROM node:20-alpine AS deps
+
+WORKDIR /app
+COPY package.json package-lock.json* ./
+RUN npm ci
+
+# ── Stage 2: build ────────────────────────────────────────────────────────────
+FROM node:20-alpine AS builder
+
+WORKDIR /app
+COPY --from=deps /app/node_modules ./node_modules
+COPY . .
+
+# NEXT_PUBLIC_API_URL is baked in at build time via docker-compose build args
+ARG NEXT_PUBLIC_API_URL=http://backend:8000
+ENV NEXT_PUBLIC_API_URL=$NEXT_PUBLIC_API_URL
+
+RUN npm run build
+
+# ── Stage 3: runtime ──────────────────────────────────────────────────────────
+FROM node:20-alpine AS runtime
+
+WORKDIR /app
+ENV NODE_ENV=production
+
+COPY --from=builder /app/public ./public
+COPY --from=builder /app/.next/standalone ./
+COPY --from=builder /app/.next/static ./.next/static
+
+EXPOSE 3000
+
+CMD ["node", "server.js"]