Fix (UI): Align reference panel and regional guidance “Use Size” behaviour with the rest of the app

[ufuksarp]

Summary

Previously, clicking Use Size in the reference panel and the regional guidance would secretly optimise the dimensions for the current model. This caused confusion because it did not align with the expected outcome or behaviour of Use Size actions in the rest of the app (such as the gallery or viewer).

This PR updates the reference panel and the regional guidance so that Use Size now follows the same recall logic and code path as the gallery and viewer.

Related Issues / Discussions

N/A

QA Instructions

• Generate Tab
  • Set a reference image.
  • For both an uncropped and a cropped reference image, click Use Size from the reference panel and confirm the resulting width/height matches Use Size from the gallery right-click menu or viewer toolbar for the same image and crop.
• Canvas Tab
  • Repeat the same comparison on canvas for both uncropped and cropped images.
• Regional Guidance
  • Repeat the same check for regional guidance, for both uncropped and cropped images.

Merge Plan

N/A (small UI behaviour change)

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)