Implement admin database stats dashboard

Add admin-only database statistics dashboard
- Introduces types for database statistics and recent additions
- Implements hooks to fetch statistics and recent additions via RPCs
- Adds UI components for stats cards and a recent additions table
- Integrates new AdminDatabaseStats page and routing under /admin/database-stats
- Updates admin sidebar and app routes to expose the new dashboard
- Enables real-time updates and export capabilities for recent additions

src/hooks/useAdminDatabaseStats.ts

@@ -0,0 +1,21 @@
+import { useQuery } from '@tanstack/react-query';
+import { supabase } from '@/integrations/supabase/client';
+import { queryKeys } from '@/lib/queryKeys';
+import type { DatabaseStatistics } from '@/types/database-stats';
+
+export function useAdminDatabaseStats() {
+  return useQuery({
+    queryKey: queryKeys.admin.databaseStats(),
+    queryFn: async () => {
+      const { data, error } = await supabase.rpc('get_database_statistics');
+
+      if (error) {
+        throw error;
+      }
+
+      return data as unknown as DatabaseStatistics;
+    },
+    staleTime: 5 * 60 * 1000, // 5 minutes
+    refetchInterval: 60 * 1000, // Auto-refetch every 60 seconds
+  });
+}