feat: Add process cancellation (Stop button) and data loss warning on page refresh

app/static/app.js

@@ -67,6 +67,17 @@ function initApp() {
     
     let isProcessingCanceled = false; // Cancellation flag
 
+    // Warn on refresh/leave while processing
+    window.addEventListener('beforeunload', (e) => {
+        // If the loading container is visible, it means processing is active
+        if (loadingContainer.style.display !== 'none' && !isProcessingCanceled) {
+            e.preventDefault();
+            // Note: Modern browsers (Chrome/Firefox) often ignore this custom text and show a standard message,
+            // but older browsers might display it.
+            e.returnValue = 'هناك صور قيد المعالجة. إذا قمت بالتحديث الآن، فسوف تفقد تقدمك.';
+        }
+    });
+
     // Stop Button Listener
     stopBtn.addEventListener('click', () => {
         isProcessingCanceled = true;