Update a single model by its current display_name.The model is looked up using the display_name query parameter. The request body contains the fields to update, which may include a new display_name.Args: request: Arbitrary model fields to update (may include new display_name). display_name: Current display name of the model (query parameter for lookup). authorization: Bearer token header used to derive identity context.Raises: HTTPException: 404 if model not found, 409 if new display_name conflicts, 500 for unexpected errors.