Replace sidebar menu with collapsible category tree showing items

config.php

@@ -45,3 +45,32 @@ $twig->addGlobal('app_name', APP_NAME);
 // Add translated confirm messages for JS
 $twig->addGlobal('delete_part_confirm', $translator->trans('Are you sure you want to delete this part?'));
 $twig->addGlobal('delete_category_confirm', $translator->trans('Are you sure you want to delete this category?'));
+
+// Build category tree for sidebar
+$db = App\Database\Database::getInstance();
+$categories = App\Models\Category::getAll($db);
+$items = App\Models\Item::getAll($db);
+
+function buildTree($categories, $items, $parentId = null) {
+    $tree = [];
+    foreach ($categories as $cat) {
+        if ($cat['parent_id'] == $parentId) {
+            $node = [
+                'id' => $cat['id'],
+                'name' => $cat['name'],
+                'children' => buildTree($categories, $items, $cat['id']),
+                'items' => []
+            ];
+            foreach ($items as $item) {
+                if ($item['category_id'] == $cat['id']) {
+                    $node['items'][] = $item;
+                }
+            }
+            $tree[] = $node;
+        }
+    }
+    return $tree;
+}
+
+$categoryTree = buildTree($categories, $items);
+$twig->addGlobal('category_tree', $categoryTree);