fix: revert echo gate, restore Chrome AEC during screen share

The echo gate architecture bypassed the serialized mic management chain
and introduced race conditions. Chrome's AEC handles echo properly for
both headphone and speaker users without custom intervention.

packages/web/src/utils/screenShare.ts

@@ -2,7 +2,6 @@ import { Room, Track } from 'livekit-client';
 import { useVoiceStore } from '../stores/voiceStore';
 import type { ScreenShareConfig } from '../stores/voiceStore';
 import { getStreamingLimits } from '../stores/settingsStore';
-import { AudioManager } from '../audio/AudioManager';
 import { wsSend } from '../hooks/useWebSocket';
 import { getPublisherPC, getMediaStreamTrack } from './livekitInternals';
 
@@ -152,9 +151,6 @@ export async function startScreenShare(room: Room): Promise<boolean> {
       return false;
     }
 
-    // Rebuild mic without AEC now that screen share is acquired
-    AudioManager.getInstance().setScreenShareActive(true);
-
     // Set content hint from builder (motion for gaming, detail for text)
     const screenPub = room.localParticipant.getTrackPublications()
       .find(p => p.source === Track.Source.ScreenShare);
@@ -194,7 +190,6 @@ export async function startScreenShare(room: Room): Promise<boolean> {
     return true;
   } catch (err) {
     console.error('[ScreenShare] Failed to start screen share:', err);
-    AudioManager.getInstance().setScreenShareActive(false);
     return false;
   }
 }
@@ -209,7 +204,6 @@ export async function stopScreenShare(room: Room): Promise<void> {
   } catch (err) {
     console.error('[ScreenShare] Failed to stop screen share:', err);
   }
-  AudioManager.getInstance().setScreenShareActive(false);
   useVoiceStore.setState({ isScreenSharing: false });
 }
 
@@ -229,7 +223,6 @@ export async function changeScreenShare(room: Room): Promise<void> {
 // ---------------------------------------------------------------------------
 
 export function handleScreenShareUnpublished(): void {
-  AudioManager.getInstance().setScreenShareActive(false);
   useVoiceStore.setState({ isScreenSharing: false });
   const { isMuted, isDeafened, isCameraOn } = useVoiceStore.getState();
   wsSend({ type: 'voice_status', isMuted, isDeafened, isCameraOn, isScreenSharing: false });