Keep the existing public class name for URL-based image input when regenerating the SDK. Map `UrlUserInput` to `ImageUserInput` during artifact generation and update the generated model and `UserInput` union accordingly.
Extend the class-name stability test to assert that `ImageUserInput` remains importable under its expected name.
GitOrigin-RevId: 6cbbd555e2e07904cc5fbc279e1e61ff089ac0a9