Request a pre-signed URL to upload a source image directly to secure cloud storage. Use the returned future_upload_file_key as the image or input_images value in any generation endpoint.

Upload flow:

1. Call this endpoint with your file's MIME type and size.
2. PUT the raw file bytes to the returned uploadUrl (no authentication headers needed — the URL is already signed).
3. Pass future_upload_file_key as the image source in your generation request.

Constraints:

• Maximum file size: 30 MB
• Supported types: jpeg, jpg, png, gif, webp, heic, heif