fix(helpdesk): clicking sidebar icon opens nav panel instead of navigating

Set href to empty string so the Helpdesk sidebar icon toggles the
navigation panel open/closed without navigating to the customers page.
Same pattern as the bookmarks module.

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

modules/helpdesk/module.php

@@ -46,7 +46,7 @@ return [
                 'key' => 'helpdesk',
                 'label' => 'Helpdesk',
                 'icon' => 'bi-headset',
-                'href' => 'helpdesk',
+                'href' => '',
                 'permission' => 'helpdesk.access',
                 'panel_template' => 'templates/aside-helpdesk-panel.phtml',
                 'details_storage' => 'aside-helpdesk-sections-v1',