a) Admin panel now respects the site's light/dark theme toggle via CSS
custom properties that respond to [data-theme='light'] on <html>.
All hardcoded dark colors replaced with semantic CSS variables.
b) Improved contrast in dark mode: secondary text changed from #666/#555
to #a0a0a0, muted text from #555 to #707070. All text is now clearly
readable against dark backgrounds.
c) Backup system was already implemented in yaml-service.ts (creates
timestamped backups in content/.backups/ before each save, keeps last
10 versions). Now the UI shows a confirmation message that a backup
was created after each successful save.
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