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

docker-compose.yml

@@ -30,7 +30,7 @@ services:
       - backend-prod
     volumes:
       - ./nginx/nginx.conf:/etc/nginx/nginx.conf:ro
-      - ./nginx/conf.d:/etc/nginx/conf.d:ro
+      - ./nginx/conf.d.prod:/etc/nginx/conf.d:ro
       - ./ssl:/etc/nginx/ssl:ro
     ports:
       - "80:80"
@@ -122,6 +122,8 @@ services:
       args:
         - NODE_ENV=production
     container_name: spotlightcam-backend-prod
+    env_file:
+      - ./backend/.env.production
     expose:
       - "3000"
     environment: