Delete Schedule Session

Schedule deletion of an existing session after the HTTP response is sent.

Args: schedule_id: Unique identifier of the session to delete. background_tasks: FastAPI response-scoped background task collector.

Returns: A message confirming that session cleanup has been queued.

Raises: HTTPException: Status 404 when the session does not exist.

Behavior: Cleanup is registered with FastAPI rather than run before responding. The cleanup routine removes the session and requests cancellation of unfinished scheduler initialization or background generation. A later request may see the session until the response background task executes.

MessageResponse(message="ok")