Fix category dates: use event.endAt as default, auto-correct if endAt < startAt

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/Controller/AccountController.php

@@ -417,6 +417,10 @@ class AccountController extends AbstractController
             $category->setEndAt(new \DateTimeImmutable($endAt));
         }
 
+        if ($category->getEndAt() < $category->getStartAt()) {
+            $category->setEndAt($category->getStartAt()->modify('+30 days'));
+        }
+
         $em->persist($category);
         $em->flush();