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/ai_execute/sync/claude/local_cli.rs

@@ -952,7 +952,7 @@ async fn gateway_marks_claude_cli_cross_format_runtime_miss_when_format_conversi
             .headers()
             .get(LOCAL_EXECUTION_RUNTIME_MISS_REASON_HEADER)
             .and_then(|value| value.to_str().ok()),
-        Some("all_candidates_skipped")
+        Some("candidate_list_empty")
     );
     let response_json: serde_json::Value = response.json().await.expect("body should parse");
     assert_eq!(response_json["error"]["type"], "http_error");
@@ -965,12 +965,7 @@ async fn gateway_marks_claude_cli_cross_format_runtime_miss_when_format_conversi
         .list_by_request_id("trace-claude-cli-openai-local-miss-123")
         .await
         .expect("request candidate trace should read");
-    assert_eq!(stored_candidates.len(), 1);
-    assert_eq!(stored_candidates[0].status, RequestCandidateStatus::Skipped);
-    assert_eq!(
-        stored_candidates[0].skip_reason.as_deref(),
-        Some("format_conversion_disabled")
-    );
+    assert!(stored_candidates.is_empty());
     assert_eq!(*public_hits.lock().expect("mutex should lock"), 0);
 
     gateway_handle.abort();