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>

frontend/Dockerfile

@@ -36,19 +36,7 @@ RUN chmod +x scripts/hooks/post-rush-install.sh && rm -rf /app/common/temp && ru
 # Use rush build to build the specific project
 RUN rush build --to @coze-studio/app
 
-# Production image stage
-FROM nginx:1.25-alpine
-
-
-# if you located in China, you can use aliyun mirror to speed up
-RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/g' /etc/apk/repositories
-# Install necessary tools for SSL configuration
-RUN apk add --no-cache bash
-
-# Copy build artifacts to nginx static directory
-COPY --from=builder /app/frontend/apps/coze-studio/dist /usr/share/nginx/html
-
-EXPOSE 8888
-
-# Start nginx
-CMD ["nginx", "-g", "daemon off;"]
+# Dist-only stage: 镜像仅用于提取构建产物，不运行任何服务
+FROM alpine:latest
+WORKDIR /app
+COPY --from=builder /app/frontend/apps/coze-studio/dist /app/dist