feat(appearance): live theme preview in site settings
Selecting an accent, theme or palette now re-themes the settings page instantly
(updates data-palette/data-theme + the --accent style block, mirroring the shell)
so you see it before saving; reverts on reload, persists on save. Also fixes a
stale 'sage' default in the palette picker -> klonkt.
Co-Authored-By: Claude <noreply@…>
![(please configure the [header_logo] section in trac.ini)](/chrome/site/your_project_logo.png){kind=logo}
