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/layout/MobileVoiceMiniBar.tsx

@@ -92,7 +92,7 @@ export function MobileVoiceMiniBar() {
         </button>
 
         <button
-          onClick={(e) => { e.stopPropagation(); leaveVoice(); }}
+          onClick={(e) => { e.stopPropagation(); leaveVoice(); const df = useVoiceStore.getState().disconnectFn; if (df) df(); }}
           className="w-8 h-8 rounded-full flex items-center justify-center bg-accent-rose/20 text-accent-rose hover:bg-accent-rose/30 transition-colors"
         >
           <svg className="w-4 h-4" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={2}>