feat: soundboard, toast notifications, robust JSON parsing

Soundboard (Web Audio API):
- 8 ambient loops: rain, wind, fire, ocean, forest, tavern, thunder, cave
- 8 one-shot SFX: sword, bow, spell, door, coins, horn, dice, footsteps
- Brown noise generation for ambient textures
- Oscillator-based SFX with frequency sweeps
- Volume slider, active state indicators with pulsing dot
- Stop All button when ambients are playing
- Toast notifications on SFX trigger

Toast notification system:
- Zustand-based store with auto-dismiss (4s)
- 4 types: success, error, info, warning
- Slide-in animation from top-right
- Dismissible with × button
- Integrated into App shell

JSON parsing (all AI components):
- Shared lib/llm-parse.ts with extractJson, parseLlmJson, flattenValue, ensureArray
- Strips markdown code fences before parsing
- Handles nested objects where strings expected
- All 5 AI components use parseLlmJson instead of raw regex
- All prompts explicitly request raw JSON with no fences
- ItemForge shows raw response in <details> on parse failure

Full production build passing

package.json

@@ -16,7 +16,8 @@
     "framer-motion": "^12",
     "lucide-react": "^0.525",
     "react": "^19.2.7",
-    "react-dom": "^19.2.7"
+    "react-dom": "^19.2.7",
+    "zustand": "^5.0.14"
   },
   "devDependencies": {
     "@tailwindcss/vite": "^4",