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/features/call/Controls.tsx

@@ -53,7 +53,7 @@ export function SoundButton({ enabled, onToggle }: SoundButtonProps) {
       delay={500}
       tooltip={
         <Tooltip>
-          <Text size="T200">{enabled ? 'Turn Off Sound' : 'Turn On Sound'}</Text>
+          <Text size="T200">{enabled ? 'Deafen' : 'Undeafen'}</Text>
         </Tooltip>
       }
     >