- Introduce soundtrack override system allowing games to define custom music
- Add Nintendo-themed soundtrack for Super Kart (2 tracks with metadata)
- Make main menu track configurable via data/music.json instead of hardcoded
- Add MusicPlayer volume parameter for per-soundtrack volume control
- Lazy-load per-game audio assets via assetManifest on game entry
- Add SPACE/X keyboard shortcuts to advance Super Kart menus
- Play kart-spinner SFX when player picks up an item in Super Kart
- Increase speech queue volume to 1.0
- Add Super Kart icons artwork and additional music assets
