feat: store original EXIF-stripped image for debugging

- Save original image before crop/rotation with '_debug_original' variant
- Store original_photo_path in labels_data.image_processing for debug access
- Update DebugRotationPanel to display original image instead of processed
- Update ItemDetailModal to pass original image path to debug panel
- Enables accurate crop/rotation visualization with true original image

frontend/components/ItemDetailModal.tsx

@@ -198,6 +198,19 @@ export default function ItemDetailModal({
         <DebugRotationPanel
           item={item}
           imageUrl={buildPhotoUrl(backendUrl, currentPhoto.full_url)}
+          originalPhotoPath={
+            item.labels_data
+              ? (() => {
+                  try {
+                    const parsed = JSON.parse(item.labels_data);
+                    const origPath = parsed.image_processing?.original_photo_path;
+                    return origPath ? buildPhotoUrl(backendUrl, origPath) : undefined;
+                  } catch {
+                    return undefined;
+                  }
+                })()
+              : undefined
+          }
           originalCropBounds={item.labels_data ? JSON.parse(item.labels_data).image_processing?.crop_bounds : undefined}
           originalRotation={item.labels_data ? JSON.parse(item.labels_data).image_processing?.rotation_degrees : undefined}
           imageProcessing={item.labels_data ? JSON.parse(item.labels_data).image_processing : undefined}