[Feature]: Add Audio Mute Button to WebRTC screen sharing in client settings

### Problem Statement

The client currently supports WebRTC screen sharing with audio, but there is no way for the user to mute the shared audio without stopping screen sharing entirely.

### Proposed Solution

Add a Mute Audio button to the screen-sharing controls.

Allow users to mute/unmute the shared audio independently.
Screen sharing and video should continue normally while audio is muted.
The button should clearly indicate the current audio state.

### Alternatives Considered (Optional)

Nil

### Additional Context (Optional)

The feature should integrate with the existing WebRTC screen-sharing controls without changing the current screen-sharing workflow.

### Checklist

- [x] I have searched for existing feature requests to avoid duplicates

Start at the existing WebRTC screen-sharing controls in client settings and trace how shared audio is managed. Add the mute/unmute control without interrupting screen sharing or video, make its visual state clear, and verify that the existing sharing workflow still works in both audio states.

Written by the indexing model from the issue text.