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/executor/outcome.rs

@@ -275,10 +275,13 @@ pub(crate) async fn record_failed_usage_for_exhausted_request(
     );
     data.request_metadata = Some(Value::Object(request_metadata));
 
-    state.usage_runtime.submit_terminal_event(
-        state.data.as_ref(),
-        UsageEvent::new(UsageEventType::Failed, request_id, data),
-    );
+    state
+        .usage_runtime
+        .record_terminal_event(
+            state.data.as_ref(),
+            UsageEvent::new(UsageEventType::Failed, request_id, data),
+        )
+        .await;
 }
 
 pub(crate) async fn record_failed_usage_for_runtime_miss_request(
@@ -406,10 +409,13 @@ pub(crate) async fn record_failed_usage_for_runtime_miss_request(
     data.request_metadata =
         (!request_metadata.is_empty()).then_some(Value::Object(request_metadata));
 
-    state.usage_runtime.submit_terminal_event(
-        state.data.as_ref(),
-        UsageEvent::new(UsageEventType::Failed, request_id, data),
-    );
+    state
+        .usage_runtime
+        .record_terminal_event(
+            state.data.as_ref(),
+            UsageEvent::new(UsageEventType::Failed, request_id, data),
+        )
+        .await;
 }
 
 fn select_last_failed_request_candidate(