Implement monitoring overview features

Add comprehensive monitoring dashboard scaffolding:
- Extend queryKeys with monitoring keys
- Create hooks: useCombinedAlerts, useRecentActivity, useDatabaseHealth, useModerationHealth
- Build UI components: SystemHealthStatus, CriticalAlertsPanel, MonitoringQuickStats, RecentActivityTimeline, MonitoringNavCards
- Create MonitoringOverview page and integrate routing (MonitoringOverview route)
- Wire AdminSidebar to include Monitoring navigation
- Introduce supporting routing and admin layout hooks/utilities
- Align with TanStack Query patterns and plan for auto-refresh and optimistic updates

src/hooks/useSystemHealth.ts

@@ -1,15 +1,18 @@
-import { useQuery } from '@tanstack/react-query';
+import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
 import { supabase } from '@/lib/supabaseClient';
 import { handleError } from '@/lib/errorHandler';
+import { toast } from 'sonner';
 
-interface SystemHealthData {
+export interface SystemHealthData {
   orphaned_images_count: number;
   critical_alerts_count: number;
+  high_alerts_count?: number;
+  failed_webhook_count?: number;
   alerts_last_24h: number;
   checked_at: string;
 }
 
-interface SystemAlert {
+export interface SystemAlert {
   id: string;
   alert_type: 'orphaned_images' | 'stale_submissions' | 'circular_dependency' | 'validation_error' | 'ban_attempt' | 'upload_timeout' | 'high_error_rate';
   severity: 'low' | 'medium' | 'high' | 'critical';
@@ -101,8 +104,10 @@ export function useSystemAlerts(severity?: 'low' | 'medium' | 'high' | 'critical
  * Only accessible to admins
  */
 export function useRunSystemMaintenance() {
-  return async () => {
-    try {
+  const queryClient = useQueryClient();
+  
+  return useMutation({
+    mutationFn: async () => {
       const { data, error } = await supabase.rpc('run_system_maintenance');
 
       if (error) {
@@ -118,12 +123,18 @@ export function useRunSystemMaintenance() {
         status: 'success' | 'error';
         details: Record<string, any>;
       }>;
-    } catch (error) {
+    },
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['system-health'] });
+      queryClient.invalidateQueries({ queryKey: ['system-alerts'] });
+      toast.success('System maintenance completed successfully');
+    },
+    onError: (error) => {
       handleError(error, {
         action: 'Run System Maintenance',
         metadata: { error: String(error) }
       });
-      throw error;
-    }
-  };
+      toast.error('Failed to run system maintenance');
+    },
+  });
 }