refactor: extract admin business logic to services, introduce job queue, add derived index helpers

- Move DB operations from routes/admin.py to services/admin.py (get_logs_context, query_summary_statuses, retry_failed, delete/reset operations)
- Add services/jobs.py with Job/JobEvent-based async job queue (create_job, run_job, enqueue_job)
- Add services/derived.py with FTS5 reindex and paper index deletion helpers
- Refactor scheduler to use job queue instead of direct pipeline calls
- Add heartbeat_at/expires_at to TaskLock for lock health tracking
- Remove DESIGN_REVIEW.md
- Update tests: remove redundant integration tests, add unit tests for new services

app/database.py

@@ -76,10 +76,26 @@ def _migrate(engine) -> None:
         "crawl_logs": [
             ("details_json", "TEXT"),
         ],
+        "task_locks": [
+            ("heartbeat_at", "DATETIME"),
+            ("expires_at", "DATETIME"),
+        ],
+        "jobs": [
+            ("heartbeat_at", "DATETIME"),
+        ],
     }
 
     with engine.connect() as conn:
         for table, columns in _MIGRATIONS.items():
+            table_exists = conn.execute(
+                text(
+                    "SELECT name FROM sqlite_master "
+                    "WHERE type IN ('table', 'virtual table') AND name = :name"
+                ),
+                {"name": table},
+            ).fetchone()
+            if not table_exists:
+                continue
             # 获取已有列名
             existing = {
                 row[1] for row in conn.execute(text(f"PRAGMA table_info({table})"))