feat(audio): Haus ambient sounds + YouTube player fix

WhiteNoise replaced with full ambient mixer:
- 6 categories: Noise, Rain, Nature, Places, Things, Animals
- 29 real ambient sounds from Haus (MIT licensed)
- Howler.js for playback with looping and per-sound volume
- Mix multiple sounds simultaneously
- Category tab navigation
- 300ms fade in/out for smooth toggling

MusicPlayer fixes:
- Removed origin param (causes issues behind reverse proxy)
- Added onError handler for YouTube errors
- Added onStateChange to track playing state
- Player container 1x1 opacity:0 instead of offscreen positioning

frontend/package.json

@@ -9,6 +9,7 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "howler": "^2.2.4",
     "pixi-live2d-display": "^0.4.0",
     "pixi.js": "^7.4.3",
     "react": "^19.2.6",
@@ -16,13 +17,14 @@
   },
   "devDependencies": {
     "@tailwindcss/vite": "^4.1.6",
+    "@types/howler": "^2.2.13",
     "@types/react": "^19.2.14",
     "@types/react-dom": "^19.2.3",
     "@vitejs/plugin-react": "^6.0.1",
     "autoprefixer": "^10.4.20",
     "postcss": "^8.5.3",
     "tailwindcss": "^4.1.6",
-    "typescript": "~6.0.2",
+    "typescript": "^6.0.3",
     "vite": "^8.0.12"
   }
 }