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/hooks/callPreferences.ts

@@ -1,6 +1,8 @@
 import { createContext, useCallback, useContext } from 'react';
 import { useAtom } from 'jotai';
 import { CallPreferences, CallPreferencesAtom } from '../callPreferences';
+import { useSetting } from './settings';
+import { settingsAtom } from '../settings';
 
 const CallPreferencesAtomContext = createContext<CallPreferencesAtom | null>(null);
 export const CallPreferencesProvider = CallPreferencesAtomContext.Provider;
@@ -21,6 +23,7 @@ export const useCallPreferences = (): CallPreferences & {
 } => {
   const callPrefAtom = useCallPreferencesAtom();
   const [pref, setPref] = useAtom(callPrefAtom);
+  const [cameraOnJoin] = useSetting(settingsAtom, 'cameraOnJoin');
 
   const toggleMicrophone = useCallback(() => {
     const microphone = !pref.microphone;
@@ -54,6 +57,7 @@ export const useCallPreferences = (): CallPreferences & {
 
   return {
     ...pref,
+    video: cameraOnJoin ? pref.video : false,
     toggleMicrophone,
     toggleVideo,
     toggleSound,