fix: address pr-bug-scan findings from #1429

Narrowed App.tsx theme useEffect dependency from full settings object to settings?.theme so unrelated settings mutations no longer re-run applyDocumentTheme and kill in-progress UI transitions.

src/renderer/src/App.tsx

@@ -514,7 +514,7 @@ function App(): React.JSX.Element {
       mq.addEventListener('change', handler)
       return () => mq.removeEventListener('change', handler)
     }
-  }, [settings])
+  }, [settings?.theme])
 
   useEffect(() => {
     document.documentElement.style.setProperty(