fix(config): clear the old category cache on upgrade

The old cache is only replaced when the categories are requested, so
on instances that use a menu without categories the 170 KB app config
value stayed and was still loaded on every request. A post-migration
repair step clears it when the app is upgraded.

lib/Migration/ClearCategoryCache.php

@@ -0,0 +1,46 @@
+<?php
+
+/**
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+namespace OCA\SideMenu\Migration;
+
+use OCA\SideMenu\Service\CategoryRepository;
+use OCP\Migration\IOutput;
+use OCP\Migration\IRepairStep;
+
+/**
+ * Earlier versions stored the category cache as a regular app config
+ * value, which Nextcloud loads on every request. Clear it on upgrade so
+ * it does not linger on instances that never request the categories.
+ */
+class ClearCategoryCache implements IRepairStep
+{
+    public function __construct(protected CategoryRepository $categoryRepository)
+    {
+    }
+
+    public function getName(): string
+    {
+        return 'Clear the category cache';
+    }
+
+    public function run(IOutput $output): void
+    {
+        $this->categoryRepository->clearCache();
+    }
+}