add element siblings

backend/app/Element/UseCases/GetElement/GetElement.php

@@ -27,10 +27,19 @@ class GetElement
             throw new NotFoundException('Element not found');
         }
 
+        $parentElement = $element->getParentElement();
+        if ($parentElement === null) {
+            $siblingElements = [$element];
+        } else {
+            $siblingElements = $this->elementRepository
+                ->findByParentElement($parentElement);
+        }
+
         return new GetElementResult(
             element: $element,
             childElements: $this->elementRepository
                 ->findByParentElement($element),
+            siblingElements: $siblingElements,
         );
     }
 }