v0.6.4

feat: add accessibility TTS support and enhance key button UI

- Bump version to 0.6.4 (AssemblyVersion, FileVersion, Version)
- Add System.Speech package for text-to-speech functionality
- Register AccessibilityService in DI container for TTS features
- Update KeyButton.xaml with improved lock icon visibility (collapsed state)
- Add StickyBadge control for sticky mode indicator (size: 9, bottom alignment)
- Clean up outdated configuration file references and encoding artifacts