feat: Add Asteroids game article with full implementation

Complete browser-native Asteroids game built with Scittle and ClojureScript.

Key features:
- Physics simulation with momentum and wrap-around
- Asteroid splitting mechanics (large/medium/small)
- UFO enemies with targeting AI
- Hyperspace jump (10% risk)
- Canvas vector graphics
- Particle effects
- Progressive difficulty
- High score tracking

Implementation uses keyword arguments throughout, Reagent atoms for state,
and Canvas API for rendering. Zero build tools required - runs directly in
the browser via Scittle.

Includes comprehensive article with architecture diagrams, code examples,
and extension ideas for learning game development concepts.

Author: burinc