feat: 定时任务运行详情执行过程视图 + 管理员下载删除 + MySQL 迁移修复

定时任务:
- 运行详情页新增「执行过程」标签页,按 agent_run_id 拉取该次运行的
  agent 消息(GET /scheduled-tasks/runs/{id}/messages),运行中每 4s
  自动刷新,可观察卡住的任务停在哪一步
- 详情页「返回」按钮回到来源列表(普通/管理员)并重新选中原任务
- 管理员可下载、删除任意用户的执行记录(DELETE /runs/{id} 加管理员兜底)

MySQL 兼容修复:
- 合并迁移 20260518_06 汇合 ai-writing 与 thread-shares 两个 head
- 20260517_02 改用 SQLAlchemy Core 构造,规避保留字 key 的 1064 报错
- list_messages_by_run 各事件存储补 user_id 形参以保持接口一致

测试: 新增 test_scheduled_task_admin_run_delete.py

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

offline-backend-20260512/backend/CLAUDE.md

@@ -227,7 +227,7 @@ FastAPI application on port 8001 with health check at `GET /health`. Set `GATEWA
 | **Runs** (`/api/runs`) | `POST /stream` - stateless run + SSE; `POST /wait` - stateless run + block; `GET /{rid}/messages` - paginated messages by run_id `{data, has_more}` (cursor: `after_seq`/`before_seq`); `GET /{rid}/feedback` - list feedback by run_id |
 | **Thread Shares** (`/api/thread-shares`) | Per-conversation sharing with two modes (`thread_shares.mode`). **`import`**: `POST /` `{thread_id, mode}` - create (or reuse) a revocable share code; `GET /{code}/preview` + `POST /{code}/import` - copy that conversation into the caller's account (fresh `thread_id` via `app/gateway/thread_copy.py` + new `threads_meta` row + `user-data` copy; dedup on `metadata.shared_origin`). **`view`**: a public, read-only static page — see Public Shares below. Both modes: `GET /` - list my codes; `DELETE /{code}` - revoke. |
 | **Public Shares** (`/api/public/shares`) | **Unauthenticated** (the `/api/public/` prefix is whitelisted in `auth_middleware._PUBLIC_PATH_PREFIXES`). `GET /{code}` - read-only conversation snapshot (title + serialized messages + artifacts) for a `view`-mode share; messages are read straight from the latest checkpoint. `GET /{code}/files/{path}` - serves an **image** referenced by that conversation (images only — non-image paths 404; SVG forced to download). Missing/revoked/non-`view` codes all return 404. |
-| **Scheduled Tasks** (`/api/scheduled-tasks`) | Per-user cron-like agent tasks. `GET/POST /` - list/create owned tasks; `PATCH/DELETE /{id}` - update/delete (owner); `POST /{id}/{pause,resume,trigger}`; `GET /{id}/runs`, `GET/DELETE /runs/{rid}`, run-file preview/edit/download; publish/subscribe under `/{id}/{publish,unpublish,subscribe}` and `GET /published`. **Admin (cross-user):** `GET /admin/all` - every task; `PATCH/DELETE /admin/{id}` - edit/delete any task; `POST /admin/{id}/trigger`; `GET /admin/{id}/runs`. Admin routes require `system_role == "admin"`. |
+| **Scheduled Tasks** (`/api/scheduled-tasks`) | Per-user cron-like agent tasks. `GET/POST /` - list/create owned tasks; `PATCH/DELETE /{id}` - update/delete (owner); `POST /{id}/{pause,resume,trigger}`; `GET /{id}/runs`, `GET /runs/{rid}`, run-file preview/edit/download; `GET /runs/{rid}/messages` - agent messages for the run's underlying agent run (used to inspect a stuck/running run; authorized via `_load_run`); `DELETE /runs/{rid}` - owner-scoped, with an admin fallback so admins can delete any user's run; publish/subscribe under `/{id}/{publish,unpublish,subscribe}` and `GET /published`. **Admin (cross-user):** `GET /admin/all` - every task; `PATCH/DELETE /admin/{id}` - edit/delete any task; `POST /admin/{id}/trigger`; `GET /admin/{id}/runs`. Admin routes require `system_role == "admin"`. |
 
 Proxied through nginx: `/api/langgraph/*` → LangGraph, all other `/api/*` → Gateway.