Add mobile touch controls and fix performance bugs

Mobile Support:
- Virtual joystick for rotation and thrust
- FIRE and HYPER touch buttons with visual feedback
- Touch event handling (touchstart, touchmove, touchend)
- Scittle-compatible touch ID tracking (avoid array-seq)

Performance Fixes:
- Fix exponential asteroid explosion from rapid firing
- Batch collision detection to prevent duplicate hits
- Add limits: 50 asteroids max, 200 particles max
- Reduce particle counts per explosion (50% reduction)
- Maintain 60 FPS on desktop and mobile

Article:
- Document mobile controls implementation
- Explain performance bug and solutions
- Update metadata and instructions

Driven by kids wanting to play on phones and discovering the
rapid-fire bug through testing. Now works smoothly cross-platform.

Author: burinc