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/CallControls.tsx

@@ -235,7 +235,7 @@ export function CallControls({ callEmbed }: CallControlsProps) {
               <Text size="B300">Share</Text>
             </Button>
             <Button
-              size="300" variant="Surface" fill="Soft" radii="300" outlined
+              size="300" variant="Secondary" fill="Soft" radii="300" outlined
               onClick={() => setShareConfirm(false)}
             >
               <Text size="B300">Cancel</Text>