[SandObserver]

Summary

• Report toast.saved from the Appearance save instead of toast.wallpaperSaved, matching the toggles on the same page.
• Remove the now unreferenced toast.wallpaperSaved key from all six catalogues.
• Add a CHANGELOG entry under Unreleased.

Testing
All green, including the i18n reachability and coverage checks that pin the catalogue keys. No new coverage needed.

Checklist

• Stays within the project constraints: one container, no runtime dependencies, no build step (see CONTRIBUTING.md).
• Tests added or updated for new logic, and the full suite, lint, and typechecks pass.
• Docs updated if behavior or configuration changed.
• CHANGELOG.md updated under Unreleased if the change is user-visible.