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/MainContent.tsx

@@ -274,7 +274,7 @@ export function MainContent() {
               <p className="text-txt-tertiary text-[15px]">No one is currently in this voice channel.</p>
             </div>
             <button
-              onClick={() => joinVoiceChannel(currentChannelId)}
+              onClick={() => joinVoiceChannel(currentChannelId, useVoiceStore.getState().connectFn ?? undefined)}
               className="relative z-10 px-8 py-3 bg-accent-primary hover:bg-accent-primary-hover text-white font-semibold rounded-full transition-all text-[15px] shadow-[0_4px_20px_rgba(124,108,246,0.3)]"
             >
               Join Voice