Introduce FrostyColors ThemeExtension with 7 semantic color fields
(highlightedMessage, emoteOnly, followersOnly, slowMode, subOnly,
uniqueMode, overlayOnSurface) and brightness-aware light/dark variants.
Replace hardcoded colors across 15 files:
- Links use colorScheme.primary instead of Colors.blue
- Mentions use colorScheme.error instead of Colors.red
- First-time chatters share highlightedMessage (Twitch purple)
- Chat mode indicators use frostyColors fields
- Overlay text uses frostyColors.overlayOnSurface
Remove Provider<FrostyThemes> pattern from main.dart, channel.dart,
video_overlay.dart, and frosty_photo_view_dialog.dart.
Replace manual onSurface.withValues(alpha: 0.6) with M3's built-in
onSurfaceVariant for secondary text in section headers, chat modes,
alerts, loading indicators, and input hints. Fix double-muted
onSurfaceVariant.withValues(alpha: 0.6) in navigation icons and
notification dismiss button.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
96bce87a0e