Support reference images for imagegen

What variant of Codex are you using?

CLI

What feature would you like to see?

Need codex CLI built-in image_gen tool can generate images with reference image files.

Currently Codex says the image_gen tool only accept 1 parameter prompt.

Expected use case is like:

> Generate a selfie using @my-ugly-photo.png @my-sleeping-photo.jpg

Additional information

_No response_