Add crop preview rectangle while dragging

croppa/main.py

@@ -680,6 +680,13 @@ class VideoEditor:
             display_frame
         )
 
+        # Draw crop selection preview during Shift+Click+Drag
+        if self.crop_preview_rect:
+            x, y, w, h = self.crop_preview_rect
+            cv2.rectangle(
+                canvas, (int(x), int(y)), (int(x + w), int(y + h)), (0, 255, 0), 2
+            )
+
         # Add info overlay
         rotation_text = (
             f" | Rotation: {self.rotation_angle}°" if self.rotation_angle != 0 else ""