Cleanup dead variables and unused imports, swap ImageBackground for Image in FrameOverlay

src/screens/PreviewScreen.tsx

@@ -71,7 +71,7 @@ export default function PreviewScreen({
 
   // Sticker state
   const [stickers, setStickers] = useState<StickerData[]>([]);
-  const [selectedImageIndex, setSelectedImageIndex] = useState<number | null>(null);
+  const [selectedStickerId, setSelectedStickerId] = useState<string | null>(null);
 
   const mountedRef = useRef(true);
   useEffect(() => {