Add template selection rectangle visualization in VideoEditor

This commit introduces a new feature in the VideoEditor that allows users to visualize the template selection rectangle on the canvas. The rectangle is drawn in magenta, enhancing the user interface and providing clearer feedback during template selection. This update complements the existing functionality for selective feature deletion and improves overall usability.

croppa/main.py

@@ -2886,6 +2886,11 @@ class VideoEditor:
             x, y, w, h = self.selective_feature_deletion_rect
             cv2.rectangle(canvas, (x, y), (x + w, y + h), (0, 0, 255), 2)  # Red for deletion
         
+        # Draw template selection rectangle
+        if self.template_selection_rect:
+            x, y, w, h = self.template_selection_rect
+            cv2.rectangle(canvas, (x, y), (x + w, y + h), (255, 0, 255), 2)  # Magenta for template selection
+        
         # Draw previous and next tracking points with motion path visualization
         if not self.is_image_mode and self.tracking_points:
             prev_result = self._get_previous_tracking_point()