refactor(task): 拆分 TaskService 并重构任务生命周期

- 将 task 公共协议/上下文/异常/schema 下沉到 core，并迁移 polling 目录
- 新增 execute/submit/video 子模块，拆分同步执行、异步提交流程、错误处理与视频任务操作
- 收敛 TaskService 为门面编排，内部委派到 SyncTaskExecutionService、AsyncTaskSubmitService、VideoTaskOperationsService
- 重构 main 生命周期管理：引入 LifecycleState，拆分启动与关闭流程
- 删除未使用的 TaskExecuteFacadeService 与 TaskSubmitFacadeService

Closes #201

Co-authored-by: AAEE86 <ppk0227@hotmail.com>

tests/services/test_video_ops_cancel_delegate.py

@@ -0,0 +1,44 @@
+from __future__ import annotations
+
+from types import SimpleNamespace
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+from fastapi import HTTPException
+
+from src.services.task.core.exceptions import TaskNotFoundError
+from src.services.task.video.operations import VideoTaskOperationsService
+
+
+@pytest.mark.asyncio
+async def test_video_ops_cancel_delegates_to_cancel_ops() -> None:
+    svc = VideoTaskOperationsService(MagicMock())
+    task = SimpleNamespace(id="task-1")
+
+    svc._get_video_task_for_user = MagicMock(return_value=task)  # type: ignore[attr-defined, method-assign]
+    svc._cancel_ops.cancel_task = AsyncMock(return_value={"ok": True})  # type: ignore[attr-defined, method-assign]
+
+    result = await svc.cancel(
+        "task-1",
+        user_id="user-1",
+        original_headers={"x-test": "1"},
+    )
+
+    assert result == {"ok": True}
+    svc._cancel_ops.cancel_task.assert_awaited_once_with(  # type: ignore[attr-defined]
+        task=task,
+        task_id="task-1",
+        original_headers={"x-test": "1"},
+    )
+
+
+@pytest.mark.asyncio
+async def test_video_ops_cancel_maps_not_found_to_http_404() -> None:
+    svc = VideoTaskOperationsService(MagicMock())
+    svc._get_video_task_for_user = MagicMock(side_effect=TaskNotFoundError("missing"))  # type: ignore[attr-defined, method-assign]
+
+    with pytest.raises(HTTPException) as excinfo:
+        await svc.cancel("missing", user_id="user-1")
+
+    assert excinfo.value.status_code == 404
+    assert excinfo.value.detail == "Video task not found"