Implements spec `099-alerts-v1-teams-email`.
- Monitoring navigation: Alerts as a cluster under Monitoring; default landing is Alert deliveries.
- Tenant panel: Alerts points to `/admin/alerts` and the cluster navigation is hidden in tenant panel.
- Guard compliance: removes direct `Gate::` usage from Alert resources so `NoAdHocFilamentAuthPatternsTest` passes.
Verification:
- Full suite: `1348 passed, 7 skipped` (EXIT=0).
Co-authored-by: Ahmed Darrazi <ahmed.darrazi@live.de>
Reviewed-on: #121
