Optimize cycle detection with isset() for O(1) lookup performance

Co-authored-by: thorsten <45284+thorsten@users.noreply.github.com>

Author: Copilot

phpmyfaq/src/phpMyFAQ/Category/Order.php

@@ -138,12 +138,12 @@ public function getCategoryTree(array $categories, int $parentId = 0, array &$vi
 
             if ($categoryParentId === $parentId) {
                 // Check if this category has already been visited to prevent cycles
-                if (in_array($categoryId, $visited, true)) {
+                if (isset($visited[$categoryId])) {
                     continue;
                 }
 
                 // Add current category to visited list
-                $visited[] = $categoryId;
+                $visited[$categoryId] = true;
 
                 $childCategories = $this->getCategoryTree($categories, $categoryId, $visited);
                 $result[$categoryId] = $childCategories;