feat: implement complete score tracking system

- Track score (starts at 0)
- +1 score and +1 correct for each correct character typed
- -1 score and +1 missed for each wrong character typed
- +1 deaths for each collision with ship
- Score resets when game starts
- All metrics exposed through ScoreManager
- Updated example app UI with colorful scoreboard showing:
  - Time (gray)
  - Score (neutral)
  - Correct (green)
  - Missed (yellow)
  - Deaths (red)
  - Keystrokes (neutral)
- Uses grid layout for organized metric display
- Score cannot go below 0 (clamped to minimum)

package.json

@@ -46,6 +46,7 @@
     "dist"
   ],
   "scripts": {
+    "dev": "cd example && bun run dev",
     "build": "tsc --outDir dist --declaration --emitDeclarationOnly false && node -e \"const fs = require('node:fs'); fs.mkdirSync('dist', { recursive: true }); fs.copyFileSync('src/game.css', 'dist/game.css'); fs.copyFileSync('package.json', 'dist/package.json');\"",
     "prepublishOnly": "npm run build"
   },