[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.

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