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/utils/voiceActions.ts

@@ -85,7 +85,7 @@ export async function handleScreenShareAction(): Promise<void> {
  */
 export function handleDisconnectAction(): void {
   const voice = useVoiceStore.getState();
-  const { activeDmCall, currentVoiceChannelId } = voice;
+  const { activeDmCall, currentVoiceChannelId, disconnectFn } = voice;
 
   if (activeDmCall) {
     wsSend(
@@ -99,6 +99,9 @@ export function handleDisconnectAction(): void {
     voice.leaveVoice();
   }
 
+  // Tear down the LiveKit connection
+  if (disconnectFn) disconnectFn();
+
   // Exit fullscreen if active
   const voiceFullscreen = useUIStore.getState().voiceFullscreen;
   if (voiceFullscreen) {