Phase 2 frontend: voice store, VoiceChannel, VoicePanel, VoiceControls

Frontend:
- stores/voice.ts: Zustand store for voice state (join, leave, mute, deafen, video, screen share)
- VoiceChannel.tsx: sidebar item showing 🔊 channel name with participant count
- VoicePanel.tsx: box-drawn frame with participant list and controls
- VoiceControls.tsx: [m] mute, [d] deafen, [cam] video, [share] screen, [x] disconnect
- ChannelList.tsx: integrated VoiceChannel for voice-type channels
- Layout.tsx: added VoicePanel above chat area

Deps:
- Added livekit-client, @livekit/components-react
- NODE_ENV fix for dev deps installation

web/package.json

@@ -19,7 +19,7 @@
   },
   "devDependencies": {
     "@types/react": "^18.3.3",
-    "@types/react-dom": "^18.3.0",
+    "@types/react-dom": "^18.3.7",
     "@vitejs/plugin-react": "^4.3.1",
     "autoprefixer": "^10.4.19",
     "postcss": "^8.4.38",