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/src/components/Layout.tsx

@@ -4,6 +4,7 @@ import { useAuthStore } from '../stores/auth.ts';
 import { ServerBar } from './ServerBar.tsx';
 import { ChannelList } from './ChannelList.tsx';
 import { MemberList } from './MemberList.tsx';
+import { VoicePanel } from './VoicePanel.tsx';
 
 export function Layout() {
   const isAuthenticated = useAuthStore((state) => state.isAuthenticated);
@@ -54,7 +55,12 @@ export function Layout() {
           <ServerBar />
           <ChannelList />
           <div className="flex-1 min-w-0 flex flex-col">
-            <Outlet />
+            <div className="flex-1 min-h-0 flex flex-col overflow-hidden">
+              <VoicePanel />
+              <div className="flex-1 min-h-0">
+                <Outlet />
+              </div>
+            </div>
           </div>
           <MemberList />
         </div>