- Add data-i18n attrs to all remaining sections: download, AI plan,
sponsors, star history, footer, doc-tags
- Sync _en dictionary keys with HTML data-i18n attributes
- Fix dynamic download badge to work with i18n system
- Add View Transitions API circular reveal for theme toggle
- Light→Dark: expands from bottom-left
- Dark→Light: expands from top-right
- 700ms with Material Design easing, graceful fallback
- Remove body background/color transition (conflicts with view-transition)