Docker Multi-Stage Helper

# Build stage
FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json .
RUN npm ci --frozen-lockfile
COPY . .
RUN npm run build

# Production stage
FROM node:20-alpine AS production
WORKDIR /app
RUN addgroup -S appgroup && adduser -S appuser -G appgroup
USER appuser
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
COPY package.json .
EXPOSE 3000
CMD ["node", "dist/index.js"]

# Build: docker build -t my-app .
# Run: docker run -p 3000:3000 my-app