Admins can toggle maintenance mode from the admin dashboard (new
"Wartung" tab). When active, all non-admin users see a full-page
maintenance screen instead of the app.
- Backend: GET /api/config/service-mode endpoint (authenticated)
- Backend: stores state in app_settings key 'service_mode'
- Frontend: ServiceModeGuard wraps all ProtectedRoutes
- Frontend: ServiceModePage full-screen maintenance UI
- Frontend: ServiceModeTab in admin dashboard with toggle + message
- Admins (dashboard_admin group) always bypass the guard
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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