ci: 改为单 job 直接构建部署，消除 Gitea Registry 依赖

ci.yml: 合并为单 deploy job，runs-on aliyun，apk 安装工具，docker compose up -d --build 直接构建

docker-compose.prod.yml: backend/worker/frontend 改用 build: 块，移除 nginx bind mount

frontend/Dockerfile: 添加 ARG NGINX_CONFIG，生产构建传入 nginx.prod.conf 进镜像

frontend/Dockerfile

@@ -5,6 +5,8 @@
 #   docker build -f frontend/Dockerfile -t feedsystem-frontend .
 #
 
+ARG NGINX_CONFIG=nginx.conf
+
 FROM node:24-alpine AS build
 WORKDIR /src
 
@@ -15,7 +17,8 @@ COPY frontend/ ./
 RUN npm run build
 
 FROM nginx:1.27-alpine
-COPY frontend/nginx.conf /etc/nginx/conf.d/default.conf
+ARG NGINX_CONFIG
+COPY frontend/${NGINX_CONFIG} /etc/nginx/conf.d/default.conf
 COPY --from=build /src/dist /usr/share/nginx/html
 EXPOSE 80
 CMD ["nginx", "-g", "daemon off;"]