fix(ui): convert reference image configs when switching main model base

[Pfannkuchensack]

Summary

When switching between FLUX.2 (model-less reference images) and other models that require IP adapter/Redux models, the reference image configs were not being converted, leaving stale config types that hid or showed the wrong UI controls.

Users had to delete and re-add each reference image after switching models to get the correct UI (model selector, weights, etc.) to appear.

Related Issues / Discussions

https://discord.com/channels/1020123559063990373/1049495067846524939/1466651762210508911

QA Instructions

1. Select a FLUX.2 Klein model as main model
2. Add one or more reference images (these will be model-less flux2_reference_image configs)
3. Switch the main model to Flux.1 (or another model that uses IP adapters)
4. Verify that the reference images now show the model selector, weight slider, and other IP adapter controls without needing to delete and re-add them
5. Switch back to FLUX.2 Klein and verify the model selector disappears (configs converted back to flux2_reference_image)

Merge Plan

No special merge considerations.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• ❗Changes to a redux slice have a corresponding migration
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)

[lstein]

Works as advertised.

The main issue is that the modelSelected.ts frontend code is rapidly filling up with special case code with hard-coded specific models. I think we need to generalize this code by expanding the main model configuration definition to include hints about what type of reference image handling the main model supports.

I created issue #8815 to track this suggestion.