Implemented a level selection system with 5 difficulty modes (Recruit, Pilot, Captain, Commander, Test), each with different asteroid counts, sizes, speeds, and constraints. Upgraded BabylonJS from 7.13.1 to 8.32.0 and fixed particle system animation compatibility issues.
- Add card-based level selection UI with 5 difficulty options
- Create difficulty configuration system in Level1
- Fix explosion particle animations for mesh emitters (emitter.y → emitter.position.y)
- Implement particle system pooling for improved explosion performance
- Upgrade @babylonjs packages to 8.32.0
- Fix audio engine unlock after Babylon upgrade
- Add test mode with 100 large, slow-moving asteroids
- Add styles.css for level selection cards with hover effects
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
