Get job status

Poll the status of an async generation job. Status transitions through `pending` → `processing` → `completed` or `failed`. When completed, the `result` object contains output URLs (see each endpoint's documentation for the available keys). Poll every 5 seconds and stop when the status reaches `completed` or `failed`. Status and output URLs are available for 24 hours after the job reaches a terminal state. After expiry this endpoint returns `404`.