Refactor: Add missing countdownTimerRef cleanup and top-level mounted guards

src/screens/PreviewScreen.tsx

@@ -216,6 +216,7 @@ export default function PreviewScreen({
 
   // Triggers the view capture and the print job
   const handlePrint = async () => {
+    if (!mountedRef.current) return;
     if (isProcessing) return;
     setIsProcessing(true);
     setStatusMessage('Dein Foto wird vorbereitet...');
@@ -250,6 +251,7 @@ export default function PreviewScreen({
 
   // Saves to gallery without printing
   const handleSaveOnly = async () => {
+    if (!mountedRef.current) return;
     if (isProcessing) return;
     setIsProcessing(true);
     setStatusMessage('Bild wird generiert...');
@@ -277,6 +279,7 @@ export default function PreviewScreen({
 
   // Auto-save and exit
   const handleExit = useCallback(async () => {
+    if (!mountedRef.current) return;
     if (isProcessing) return;
     const state = stateRef.current;
     if (state.stickers.length === 0 && state.layout === 'single' && !state.activeFrame && state.dateOverlay === 'off') {
@@ -321,6 +324,7 @@ export default function PreviewScreen({
   }, [resetIdleTimer]);
 
   const handleRetakeClick = async () => {
+    if (!mountedRef.current) return;
     if (isProcessing) return;
     if (stickers.length > 0 || layout !== 'single' || activeFrame || dateOverlay !== 'off') {
       setIsProcessing(true);