feat(ws): 新增WebSocket实时通信支持与SSE独立服务

重构中间件结构，新增ws模块实现WebSocket流程执行实时推送
将SSE服务拆分为独立端口监听，默认8866
优化前端流式模式切换，支持WS/SSE协议选择
统一流式事件处理逻辑，完善错误处理与取消机制
更新Cargo.toml依赖，添加WebSocket相关库
调整代码组织结构，规范导入分组与注释

backend/src/main.rs

@@ -118,8 +118,18 @@ async fn main() -> anyhow::Result<()> {
     if let Some(f) = &env_file_used { tracing::info!("env file loaded: {}", f); } else { tracing::info!("env file loaded: <none>"); }
     tracing::info!("resolved APP_HOST={} APP_PORT={}", app_host, app_port);
 
-    let addr = format!("{}:{}", app_host, app_port);
-    tracing::info!("listening on {}", addr);
-    axum::serve(tokio::net::TcpListener::bind(addr).await?, app).await?;
+    let http_addr = format!("{}:{}", app_host, app_port);
+    tracing::info!("listening on {}", http_addr);
+
+    // HTTP 服务监听
+    let http_listener = tokio::net::TcpListener::bind(http_addr.clone()).await?;
+    let http_server = axum::serve(http_listener, app);
+
+    // WS 服务下沉到中间件
+    let ws_server = middlewares::ws::serve(db.clone());
+
+    // 新增：SSE 服务独立端口监听（默认 8866，可配 SSE_HOST/SSE_PORT）
+    let sse_server = middlewares::sse::serve(db.clone());
+    tokio::try_join!(http_server, ws_server, sse_server)?;
     Ok(())
 }