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/state/settings.ts

@@ -46,6 +46,11 @@ export interface Settings {
 
   chatBackground: ChatBackground;
   perMessageProfiles: boolean;
+
+  cameraOnJoin: boolean;
+  callNoiseSuppression: boolean;
+  pttMode: boolean;
+  pttKey: string;
 }
 
 const defaultSettings: Settings = {
@@ -84,6 +89,11 @@ const defaultSettings: Settings = {
 
   chatBackground: 'none',
   perMessageProfiles: false,
+
+  cameraOnJoin: false,
+  callNoiseSuppression: true,
+  pttMode: false,
+  pttKey: 'Space',
 };
 
 export const getSettings = () => {