feat: add production Docker setup with multi-stage builds

- Add production Dockerfiles for frontend and backend
  * Frontend: multi-stage build with nginx serving static files
  * Backend: multi-stage build with Prisma generation
- Create production nginx configuration (nginx/conf.d.prod/)
  * Routes to frontend-prod:80 and backend-prod:3000
  * Supports WebSocket connections for Socket.IO
- Update docker-compose.yml to use production config
  * Add env_file support for backend-prod
  * Mount production nginx config directory
- Add .env.production.example template for deployment

frontend/Dockerfile.prod

@@ -0,0 +1,36 @@
+# Multi-stage build for production
+
+# Stage 1: Build
+FROM node:20-alpine AS builder
+
+WORKDIR /app
+
+# Copy package files
+COPY package*.json ./
+
+# Install dependencies
+RUN npm ci --only=production --ignore-scripts
+
+# Copy all dependencies for build (including devDependencies)
+RUN npm install
+
+# Copy project files
+COPY . .
+
+# Build the application
+RUN npm run build
+
+# Stage 2: Production
+FROM nginx:alpine
+
+# Copy built assets from builder stage
+COPY --from=builder /app/dist /usr/share/nginx/html
+
+# Copy nginx configuration (if needed)
+# COPY nginx.conf /etc/nginx/conf.d/default.conf
+
+# Expose port
+EXPOSE 80
+
+# Start nginx
+CMD ["nginx", "-g", "daemon off;"]