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/ChannelSidebar.tsx

@@ -403,7 +403,8 @@ export function ChannelSidebar() {
       navigate(`/channels/${currentSpaceId}/${channelId}`);
       return;
     }
-    joinVoiceChannel(channelId);
+    const connectFn = useVoiceStore.getState().connectFn;
+    joinVoiceChannel(channelId, connectFn ?? undefined);
     navigate(`/channels/${currentSpaceId}/${channelId}`);
   };