refactor(vtt-thumbnail): [PKG-VTT-THUMB-03] own pending requests and preview resources

refactor/tasks.json

@@ -1897,11 +1897,14 @@
         "CORE-09",
         "CORE-19"
       ],
-      "status": "todo",
+      "status": "doing",
       "risk": "M",
       "deliverable": "纯解析/区间查找与 DOM、请求/定时器生命周期分离",
       "acceptance": "结构变化和缺陷修复分开记录；原 API/事件/资源生命周期通过",
-      "evidence": []
+      "evidence": [
+        "changes/2026-09-13-PKG-VTT-THUMB-03-resources.md",
+        "baselines/vtt-thumbnail-resources.json"
+      ]
     },
     {
       "id": "PKG-VTT-THUMB-04",