feat: mute screenshare audio independently + fix CI lint/prettier

- Add screenshareAudioMuted state to CallControlState and CallControl
- setSound() now preserves screenshare audio mute when un-deafening
- Add toggleScreenshareAudio() targeting audio[data-lk-source="screen_share_audio"]
- Add ScreenshareAudioButton (volume icon, warns when muted) to controls bar
- Fix unused prevScreenshare variable (ESLint error from prior commit)
- Run Prettier on Controls.tsx and CallControl.ts (CI formatting failures)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/plugins/call/CallControlState.ts

@@ -9,17 +9,21 @@ export class CallControlState {
 
   public readonly spotlight: boolean;
 
+  public readonly screenshareAudioMuted: boolean;
+
   constructor(
     microphone: boolean,
     video: boolean,
     sound: boolean,
     screenshare = false,
     spotlight = false,
+    screenshareAudioMuted = false,
   ) {
     this.microphone = microphone;
     this.video = video;
     this.sound = sound;
     this.screenshare = screenshare;
     this.spotlight = spotlight;
+    this.screenshareAudioMuted = screenshareAudioMuted;
   }
 }