Introduce lazy loading for game-specific artwork to reduce startup time.
Game assets are now defined in src/data/assetManifest.js and loaded on
first entry via src/services/assetLoader.js, replacing the previous
approach of loading all game art in PreloadScene.
Balatro improvements:
- Add bump/shake animation to chips and mult counters on score changes
- Animate round score flying into the left-bar readout with explosion
- Fix tween cleanup during view swaps to prevent crashes
- Add planetSheet artwork path to balatro-artwork.json
