refactor: extract nginx to standalone nginx-gateway deployment

- Remove coze-web service from docker-compose.yml
- Replace nginx second stage in frontend/Dockerfile with alpine dist-only stage
- Add nginx-gateway/ with standalone nginx container deployment
  - docker-compose.yml joining both coze-network and kong-net
  - Split nginx configs into 6 per-domain files:
    - 00-upstreams.conf (shared upstreams)
    - 10-default-server.conf (catch-all 444)
    - 20-coze.conf (coze studio)
    - 30-kong-api.conf (kong ai gateway)
    - 40-admin-portal.conf (admin portal)
    - 50-grafana.conf (grafana dashboard)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docker/docker-compose.yml

@@ -436,28 +436,6 @@ services:
         condition: service_healthy
     command: ['/app/opencoze']
 
-  coze-web:
-    # build:
-    #   context: ..
-    #   dockerfile: frontend/Dockerfile
-    image: cozedev/coze-studio-web:latest
-    container_name: coze-web
-    restart: always
-    ports:
-      - "8888:80"
-      - "443:443"  # SSL port (uncomment if using SSL)
-    volumes:
-      - ./nginx/nginx.conf:/etc/nginx/nginx.conf:ro  # Main nginx config
-      - ./nginx/conf.d/default.conf:/etc/nginx/conf.d/default.conf:ro  # Proxy config
-      - ./nginx/ssl:/etc/nginx/ssl:ro  # SSL certificates (uncomment if using SSL)
-      - /etc/localtime:/etc/localtime:ro
-      - /etc/timezone:/etc/timezone:ro
-    depends_on:
-      - coze-server
-      - minio
-    networks:
-      - coze-network
-
 networks:
   coze-network:
     external: true