feat: gesture-aware voice connection, remove AppLayout auto-connect

Replace the useEffect-based auto-connect pattern in AppLayout with
direct connect/disconnect calls from user gesture contexts. This is
required for iOS (AudioContext.resume + getUserMedia must happen in
a gesture handler) and aligns with tightening autoplay policies on
desktop browsers.

Architecture:
- voiceStore gains connectFn/disconnectFn refs, registered by AppLayout
  from the single useLiveKit() instance.
- All voice join paths (ChannelSidebar, MobileSpacesScreen, MainContent,
  voice_moved WS handler) pass connectFn to joinVoiceChannel().
- All disconnect paths (VoiceControls, voiceActions, MobileVoiceFullScreen,
  MobileVoiceMiniBar, dm_call_ended/rejected WS handlers, ready handler)
  call disconnectFn() directly.
- dm_call_accepted WS handler calls connectFn() to initiate the DM call
  LiveKit connection.
- The 55-line auto-connect useEffect and lastAttemptedRef are removed.

packages/web/src/components/voice/VoiceControls.tsx

@@ -75,7 +75,7 @@ export function VoiceControls() {
   };
 
   const handleDisconnect = () => {
-    const { activeDmCall } = useVoiceStore.getState();
+    const { activeDmCall, disconnectFn } = useVoiceStore.getState();
     if (activeDmCall) {
       wsSend({ type: 'dm_call_end', dmChannelId: activeDmCall.dmChannelId }, getChannelOrigin(activeDmCall.dmChannelId));
       useVoiceStore.getState().setActiveDmCall(null);
@@ -83,6 +83,7 @@ export function VoiceControls() {
       wsSend({ type: 'voice_leave' }, voiceOrigin);
       useVoiceStore.getState().leaveVoice();
     }
+    if (disconnectFn) disconnectFn();
   };
 
   const statusColor = connectionError