fix: VideoButton disabled state, PTT listener leak, TS prop errors

- VideoButton now accepts disabled prop with tooltip and visual feedback;
  PrescreenControls passes disabled=true when cameraOnJoin=false
- PTT key listener in settings tracked via ref, cleaned up on unmount,
  guarded against stacking on double-click; useCallback + useRef
- CallControls screenshare cancel button: variant Surface -> Secondary
- General.tsx Box align prop: align -> alignItems (TS2322 fix)

src/app/features/call/PrescreenControls.tsx

@@ -6,6 +6,8 @@ import { ChatButton, ControlDivider, MicrophoneButton, SoundButton, VideoButton
 import { useIsDirectRoom, useRoom } from '../../hooks/useRoom';
 import { useCallEmbed, useCallJoined, useCallStart } from '../../hooks/useCallEmbed';
 import { useCallPreferences } from '../../state/hooks/callPreferences';
+import { useSetting } from '../../state/hooks/settings';
+import { settingsAtom } from '../../state/settings';
 
 type MediaPermState = 'granted' | 'denied' | 'prompt' | 'unknown';
 
@@ -50,6 +52,7 @@ export function PrescreenControls({ canJoin }: PrescreenControlsProps) {
 
   const { microphone, video, sound, toggleMicrophone, toggleVideo, toggleSound } =
     useCallPreferences();
+  const [cameraOnJoin] = useSetting(settingsAtom, 'cameraOnJoin');
 
   return (
     <SequenceCard
@@ -67,7 +70,7 @@ export function PrescreenControls({ canJoin }: PrescreenControlsProps) {
       </Box>
       <ControlDivider />
       <Box shrink="No" alignItems="Inherit" justifyContent="SpaceBetween" gap="200">
-        <VideoButton enabled={video} onToggle={toggleVideo} />
+        <VideoButton enabled={video} onToggle={toggleVideo} disabled={!cameraOnJoin} />
         <ChatButton />
       </Box>
       <Box grow="Yes" direction="Column" gap="200">