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/Cargo.lock

@@ -244,6 +244,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "021e862c184ae977658b36c4500f7feac3221ca5da43e3f25bd04ab6c79a29b5"
 dependencies = [
  "axum-core",
+ "base64 0.22.1",
  "bytes",
  "form_urlencoded",
  "futures-util",
@@ -263,8 +264,10 @@ dependencies = [
  "serde_json",
  "serde_path_to_error",
  "serde_urlencoded",
+ "sha1",
  "sync_wrapper",
  "tokio",
+ "tokio-tungstenite",
  "tower",
  "tower-layer",
  "tower-service",
@@ -724,6 +727,12 @@ dependencies = [
  "syn 2.0.106",
 ]
 
+[[package]]
+name = "data-encoding"
+version = "2.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2a2330da5de22e8a3cb63252ce2abb30116bf5265e89c0e01bc17015ce30a476"
+
 [[package]]
 name = "deadpool"
 version = "0.12.3"
@@ -3654,6 +3663,18 @@ dependencies = [
  "tokio",
 ]
 
+[[package]]
+name = "tokio-tungstenite"
+version = "0.26.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a9daff607c6d2bf6c16fd681ccb7eecc83e4e2cdc1ca067ffaadfca5de7f084"
+dependencies = [
+ "futures-util",
+ "log",
+ "tokio",
+ "tungstenite",
+]
+
 [[package]]
 name = "tokio-util"
 version = "0.7.16"
@@ -3830,6 +3851,23 @@ version = "0.2.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e421abadd41a4225275504ea4d6566923418b7f05506fbc9c0fe86ba7396114b"
 
+[[package]]
+name = "tungstenite"
+version = "0.26.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4793cb5e56680ecbb1d843515b23b6de9a75eb04b66643e256a396d43be33c13"
+dependencies = [
+ "bytes",
+ "data-encoding",
+ "http",
+ "httparse",
+ "log",
+ "rand 0.9.2",
+ "sha1",
+ "thiserror",
+ "utf-8",
+]
+
 [[package]]
 name = "typeid"
 version = "1.0.3"
@@ -3954,6 +3992,12 @@ dependencies = [
  "percent-encoding",
 ]
 
+[[package]]
+name = "utf-8"
+version = "0.7.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09cc8ee72d2a9becf2f2febe0205bbed8fc6615b7cb429ad062dc7b7ddd036a9"
+
 [[package]]
 name = "utf8_iter"
 version = "1.0.4"