refactor: govern background job lifecycle

app/backend/bootstrap/runtime.py

@@ -16,12 +16,13 @@ def main(handler_class: type[Any] | None = None, service: Any | None = None) ->
     parser.add_argument("--port", type=int, default=8765)
     args = parser.parse_args()
     server = ThreadingHTTPServer((args.host, args.port), handler_class)
-    print(f"Xiaobai Review Web is running at http://{args.host}:{args.port}")
-    print("Press Ctrl+C to stop.")
     try:
+        service.start_background_jobs()
+        print(f"Xiaobai Review Web is running at http://{args.host}:{args.port}")
+        print("Press Ctrl+C to stop.")
         server.serve_forever()
     except KeyboardInterrupt:
         pass
     finally:
-        service._background_stop.set()
+        service.stop_background_jobs()
         server.server_close()