implement docker

Dockerfile

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+# ─── Stage 1: Install dependencies ──────────────────────────────────────────
+FROM node:22-alpine AS deps
+WORKDIR /app
+COPY backend/package*.json ./
+RUN npm ci --omit=dev
+
+# ─── Stage 2: Runtime ────────────────────────────────────────────────────────
+FROM node:22-alpine AS runner
+WORKDIR /app
+
+# Install dumb-init untuk proper signal handling
+RUN apk add --no-cache dumb-init
+
+# Copy dependencies dari stage deps
+COPY --from=deps /app/node_modules ./node_modules
+
+# Copy backend source
+COPY backend/ ./backend/
+
+# Copy frontend static files
+COPY frontend/ ./frontend/
+
+# Set working directory ke backend (karena server.js ada di sini)
+WORKDIR /app/backend
+
+# Non-root user untuk keamanan
+RUN addgroup -S appgroup && adduser -S appuser -G appgroup
+USER appuser
+
+EXPOSE 3000
+
+ENV NODE_ENV=production
+ENV PORT=3000
+
+# Health check (dipakai Coolify untuk monitoring)
+HEALTHCHECK --interval=30s --timeout=10s --start-period=30s --retries=3 \
+  CMD wget -qO- http://localhost:3000/health || exit 1
+
+ENTRYPOINT ["dumb-init", "--"]
+CMD ["node", "server.js"]