feat(helpdesk): add empty Dashboard page with sidebar nav item

Adds helpdesk/dashboard route, empty page/view, Overview nav group in the
sidebar, and Dashboard i18n keys (de + en). No content yet.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

modules/helpdesk/lib/Module/Helpdesk/Providers/HelpdeskLayoutProvider.php

@@ -38,6 +38,7 @@ final class HelpdeskLayoutProvider implements LayoutContextProvider
         }
 
         return ['helpdesk.nav' => [
+            'can_view_dashboard' => true,
             'can_manage_settings' => $canManageSettings,
             'can_view_team' => $canViewTeam,
             'can_view_risk_radar' => $canViewRiskRadar,