- Add AlertBanner import and render above nav (admin + active alerts only)
- Add AdminMonitoringDashboard import replacing UploadMonitoringDashboard in monitoring tab
- Add activeAlerts state (AlertEvent[]) with isAdmin-gated useEffect fetch
- Add handleAcknowledge with optimistic update and re-fetch on failure
- Remove UploadMonitoringDashboard import (replaced by AdminMonitoringDashboard)