fix(deploy): proxy /deepflow-backend/* to backend /api/* in Docker + expose deepflow ports

- next.config.js: server-side rewrites so the standalone frontend (built with
  NEXT_PUBLIC_API_URL=/deepflow-backend) can reach deepflow-backend:8000/api/*
  without CORS; target overridable via DEEPFLOW_BACKEND_HOST
- docker-compose: expose deepflow-frontend 3001:3000 and deepflow-backend 8000:8000

deepflow/web/next.config.js

@@ -40,6 +40,20 @@ const config = {
 
   // ... rest of the configuration.
   output: "standalone",
+
+  // Docker standalone 部署：把 /deepflow-backend/* 代理到 deepflow-backend 服务。
+  // 前端以 NEXT_PUBLIC_API_URL=/deepflow-backend 构建（见
+  // src/core/api/resolve-service-url.ts，直接拼 origin + /deepflow-backend/<path>），
+  // 而后端路由均带 /api 前缀（见 src/server/app.py）。由 Next 服务端补上 /api 前缀，
+  // 避免浏览器跨端口 / CORS 问题。目标地址可用 DEEPFLOW_BACKEND_HOST 覆盖。
+  async rewrites() {
+    const backendHost =
+      process.env.DEEPFLOW_BACKEND_HOST || "http://deepflow-backend:8000";
+    return [
+      { source: "/deepflow-backend/:path*", destination: `${backendHost}/api/:path*` },
+      { source: "/deepflow-backend", destination: `${backendHost}/api/` },
+    ];
+  },
 };
 
 export default withNextIntl(config);