UI redesign:

- Upgraded to Material 3 (Material You) design language
- Fixed status bar overlap on Android 15 devices
- Modernised all three screens (Metronome, Practice, Setlist) with clean card-based layouts
- Updated colour palette with a deep red primary accent
- Replaced old AppCompat toolbar with Material 3 AppBar throughout
- Improved button styles (filled, tonal, and outlined variants)
