refactor(gateway): 重构格式转换候选资格检查并优化测试基础设施

- 将 format_conversion_disabled 的过滤提前到候选遴选阶段，替代原来的 skip_reason 标记机制
- 为测试添加 execution_runtime_sync_override 直接注入支持，避免启动额外 HTTP 服务器
- 将 submit_terminal_event 改为 async record_terminal_event 确保失败用量事件可靠入库
- 新增 test_support 模块封装可重试的 loopback 端口绑定逻辑
- 前端：poolTrace 将 skipped 从隐藏状态移除，新增 buildPoolParticipatedCandidates 统一新旧链路逻辑，并将 skipped 状态色改为 foreground

apps/aether-gateway/src/tests/mod.rs

@@ -30,7 +30,7 @@ pub(super) use super::state::{AppState, FrontdoorCorsConfig};
 pub(super) use super::usage::UsageRuntimeConfig;
 
 pub(super) async fn start_server(app: Router) -> (String, tokio::task::JoinHandle<()>) {
-    let listener = tokio::net::TcpListener::bind("127.0.0.1:0")
+    let listener = crate::test_support::bind_loopback_listener()
         .await
         .expect("listener should bind");
     let addr = listener.local_addr().expect("local addr should resolve");
@@ -45,6 +45,20 @@ pub(super) async fn start_server(app: Router) -> (String, tokio::task::JoinHandl
     (format!("http://{addr}"), handle)
 }
 
+pub(super) async fn send_request(app: Router, mut request: Request) -> Response {
+    use tower::ServiceExt;
+
+    request
+        .extensions_mut()
+        .insert(axum::extract::ConnectInfo(std::net::SocketAddr::from((
+            [127, 0, 0, 1],
+            40000,
+        ))));
+    app.oneshot(request)
+        .await
+        .expect("router request should complete")
+}
+
 pub(super) fn build_router_with_execution_runtime_override(
     execution_runtime_override_base_url: impl Into<String>,
 ) -> Router {