Remove all obsolete authentication, settings, admin, and demo-related components and pages

- Eliminated redundant components, pages, and layouts related to authentication (`login`, `register`, `password-reset`, etc.), user settings, admin, and demos.
- Simplified the frontend structure by removing unused dynamic imports, forms, and test code.
- Refactored configurations and metadata imports to exclude references to removed features.
- Streamlined the project for future development and improved maintainability by discarding legacy and unused code.

frontend/src/app/[locale]/forbidden/page.tsx

@@ -0,0 +1,47 @@
+/**
+ * 403 Forbidden Page
+ * Displayed when users try to access resources they don't have permission for
+ */
+
+/* istanbul ignore next - Next.js type import for metadata */
+import type { Metadata } from 'next';
+import { Link } from '@/lib/i18n/routing';
+import { ShieldAlert } from 'lucide-react';
+import { Button } from '@/components/ui/button';
+
+export const metadata: Metadata = /* istanbul ignore next */ {
+  title: '403 - Forbidden',
+  description: 'You do not have permission to access this resource',
+};
+
+export default function ForbiddenPage() {
+  return (
+    <div className="container mx-auto px-6 py-16">
+      <div className="flex min-h-[60vh] flex-col items-center justify-center text-center">
+        <div className="mb-8 rounded-full bg-destructive/10 p-6">
+          <ShieldAlert className="h-16 w-16 text-destructive" aria-hidden="true" />
+        </div>
+
+        <h1 className="mb-4 text-4xl font-bold tracking-tight">403 - Access Forbidden</h1>
+
+        <p className="mb-2 text-lg text-muted-foreground max-w-md">
+          You don&apos;t have permission to access this resource.
+        </p>
+
+        <p className="mb-8 text-sm text-muted-foreground max-w-md">
+          This page requires administrator privileges. If you believe you should have access, please
+          contact your system administrator.
+        </p>
+
+        <div className="flex gap-4">
+          <Button asChild variant="default">
+            <Link href="/dashboard">Go to Dashboard</Link>
+          </Button>
+          <Button asChild variant="outline">
+            <Link href="/">Go to Home</Link>
+          </Button>
+        </div>
+      </div>
+    </div>
+  );
+}