fix(help-center): persist details open/closed state via localStorage

Add details_storage and details_open_active to the aside.tab_panel
slot declaration, matching the admin panel pattern. Section disclosure
state is now saved and restored across page loads.

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

modules/help-center/module.php

@@ -28,6 +28,8 @@ return [
                 'href' => '',
                 'permission' => '',
                 'panel_template' => 'templates/aside-help-panel.phtml',
+                'details_storage' => 'aside-help-sections',
+                'details_open_active' => true,
                 'order' => 900,
             ],
         ],