Built-in image_gen tool should accept explicit parameters: size, quality, output_format, filename/path

What variant of Codex are you using?

CLI

What feature would you like to see?

The current built-in image_gen tool (enabled via [features] image_generation = true) only accepts a single prompt parameter.

This forces users to cram everything into natural language, which is unreliable for:

• Exact dimensions
• Output filename / save path
• Quality settings
• Format (PNG with real transparency, WebP, etc.)

Current behavior (CLI / App)

Generate a hero banner, save as assets/hero.png

### Additional information

_No response_