Phase 2: ECS foundation — world, components, systems, bridge

- bitECS world with time tracking (delta, elapsed, tick)
- 5 components: Position, Velocity, SpriteRef, Health, ChemicalComposition
- Movement system (velocity * delta) + bounce system (boundary reflection)
- Health system with damage, healing, death detection
- Entity factory (createGameEntity/removeGameEntity)
- Phaser bridge: polling sync creates/destroys/updates circle sprites
- GameScene: 20 colored circles bouncing at 60fps
- BootScene: click-to-start transition, version bump to v0.2.0
- 39 ECS unit tests passing (74 total)

Co-authored-by: Cursor <cursoragent@cursor.com>

src/config.ts

@@ -1,5 +1,6 @@
 import Phaser from 'phaser';
 import { BootScene } from './scenes/BootScene';
+import { GameScene } from './scenes/GameScene';
 
 export const GAME_WIDTH = 1280;
 export const GAME_HEIGHT = 720;
@@ -10,7 +11,7 @@ export const gameConfig: Phaser.Types.Core.GameConfig = {
   height: GAME_HEIGHT,
   backgroundColor: '#0a0a0a',
   parent: document.body,
-  scene: [BootScene],
+  scene: [BootScene, GameScene],
   physics: {
     default: 'arcade',
     arcade: {