Fix (UI): Hide optimized image-to-image toggle from UI for Z-Image

[ufuksarp]

Summary

Hides the non-functional Optimized Image-to-Image toggle when a Z-Image model is selected.

Related Issues / Discussions

QA Instructions

• Select a Z-Image model on the Canvas tab.
• Check Image > Advanced options.
• Confirm Optimized Image-to-Image (beta) is not shown.

Merge Plan

Simple merge.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable) — N/A (one-line constant change)
• ❗Changes to a redux slice have a corresponding migration — N/A
• Documentation added / updated (if applicable) — N/A
• Updated What's New copy (if doing a release after this PR) — N/A unless you want a one-liner in release notes

[lstein]

Works as advertised. Thank you very much for your contribution!