Image Generation: Error messages not clear when providers don't support refinement

[Adi-ty]

Description

Referring to: https://core.trac.wordpress.org/ticket/64918

When users attempt to refine (edit) a generated image, they receive the error: "No models found that support image_generation for this prompt."

This error message is unclear because it doesn't explain that some AI providers may not support image refinement, what the user should do to resolve the issue or whether it's a provider configuration issue vs. a model limitation

Step-by-step reproduction instructions

1. Go to Settings > Connectors and add a valid API key for OpenAI
2. Generate image in new post using image block.
3. Refine generated image.

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except the AI plugin.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure

[dkotter]

Note for anyone following along, this error message was made more clear in #332, so this has been fixed though not released yet