Implements a Three.js meteor shower that triggers randomly every 2-5
minutes. Each shower spawns 15-40 meteors as streaking line segments
with fade-out trails, flying diagonally across the starfield.
- MeteorShower class manages spawn scheduling and per-frame updates
- Starfield background (3000 points) with slow ambient rotation
- Full Three.js scene bootstrap with renderer, camera, animation loop
- Import map for Three.js 0.183 added to index.html
- window.triggerMeteorShower() exposed for dev console testing
- Global CSS reset added to style.css for proper canvas layout
Fixes#113
