Add admin hooks, components, and tests for statistics, navigation, and access control

- Introduced `useAdminStats`, `useAdminUsers`, and `useAdminOrganizations` hooks for admin data fetching with React Query.
- Added `AdminSidebar`, `Breadcrumbs`, and related navigation components for the admin section.
- Implemented comprehensive unit and integration tests for admin components.
- Created E2E tests for admin access control, navigation, and dashboard functionality.
- Updated exports to include new admin components.

frontend/src/app/admin/settings/page.tsx

@@ -0,0 +1,62 @@
+/**
+ * Admin Settings Page
+ * System-wide settings and configuration
+ * Protected by AuthGuard in layout with requireAdmin=true
+ */
+
+/* istanbul ignore next - Next.js type import for metadata */
+import type { Metadata } from 'next';
+import Link from 'next/link';
+import { ArrowLeft } from 'lucide-react';
+import { Button } from '@/components/ui/button';
+
+/* istanbul ignore next - Next.js metadata, not executable code */
+export const metadata: Metadata = {
+  title: 'System Settings',
+};
+
+export default function AdminSettingsPage() {
+  return (
+    <div className="container mx-auto px-6 py-8">
+      <div className="space-y-6">
+        {/* Back Button + Header */}
+        <div className="flex items-center gap-4">
+          <Link href="/admin">
+            <Button variant="outline" size="icon">
+              <ArrowLeft className="h-4 w-4" />
+            </Button>
+          </Link>
+          <div>
+            <h1 className="text-3xl font-bold tracking-tight">
+              System Settings
+            </h1>
+            <p className="mt-2 text-muted-foreground">
+              Configure system-wide settings and preferences
+            </p>
+          </div>
+        </div>
+
+        {/* Placeholder Content */}
+        <div className="rounded-lg border bg-card p-12 text-center">
+          <h3 className="text-xl font-semibold mb-2">
+            System Settings Coming Soon
+          </h3>
+          <p className="text-muted-foreground max-w-md mx-auto">
+            This page will allow you to configure system-wide settings,
+            preferences, and advanced options.
+          </p>
+          <p className="text-sm text-muted-foreground mt-4">
+            Features will include:
+          </p>
+          <ul className="text-sm text-muted-foreground mt-2 max-w-sm mx-auto text-left">
+            <li>• General system configuration</li>
+            <li>• Email and notification settings</li>
+            <li>• Security and authentication options</li>
+            <li>• API and integration settings</li>
+            <li>• Maintenance and backup tools</li>
+          </ul>
+        </div>
+      </div>
+    </div>
+  );
+}