feat(call): PTT, deafen label, camera default off, screenshare confirm, noise suppression setting

- Push to Talk: keydown/keyup binds mic to configurable key (default Space)
  with visual PTT indicator and key-binding UI in Settings > General > Calls
- Camera always defaults OFF on join; cameraOnJoin setting for explicit opt-in
- Deafen button tooltip corrected to Deafen/Undeafen instead of Turn Off/On Sound
- Screenshare confirmation dialog before broadcasting to call participants
- Noise suppression toggle wired from settings through CallEmbed URL params
- CallControl.setMicrophone() public method for programmatic mic control
- Calls settings section added to General settings page

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

src/app/plugins/call/CallEmbed.ts

@@ -59,7 +59,8 @@ export class CallEmbed {
     mx: MatrixClient,
     room: Room,
     intent: ElementCallIntent,
-    themeKind: ElementCallThemeKind
+    themeKind: ElementCallThemeKind,
+    noiseSuppression = true
   ): Widget {
     const userId = mx.getSafeUserId();
     const deviceId = mx.getDeviceId() ?? '';
@@ -81,6 +82,7 @@ export class CallEmbed {
       perParticipantE2EE: room.hasEncryptionStateEvent().toString(),
       lang: 'en-EN',
       theme: themeKind,
+      noiseSuppression: noiseSuppression.toString(),
     });
 
     const widgetUrl = new URL(