docs(audio): [PKG-AUDIO-01] freeze released synchronization contract

refactor/tasks.json

@@ -1468,11 +1468,15 @@
       "dependsOn": [
         "BASE-05"
       ],
-      "status": "todo",
+      "status": "done",
       "risk": "H",
       "deliverable": "url/offset/sync、audio 实例暴露、update 与音量语义",
       "acceptance": "源码/声明/README/demo/发布包差异已登记；公开形状和版本范围冻结",
-      "evidence": []
+      "evidence": [
+        "changes/2026-09-12-PKG-AUDIO-01-contract.md",
+        "baselines/audio-track-contract.md",
+        "baselines/audio-track-release.json"
+      ]
     },
     {
       "id": "PKG-AUDIO-02",