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]/admin/layout.tsx

@@ -0,0 +1,44 @@
+/**
+ * Admin Route Group Layout
+ * Wraps all admin routes with AuthGuard requiring superuser privileges
+ * Includes sidebar navigation and breadcrumbs
+ */
+
+import type { Metadata } from 'next';
+import { AuthGuard } from '@/components/auth';
+import { Header } from '@/components/layout/Header';
+import { Footer } from '@/components/layout/Footer';
+import { AdminSidebar, Breadcrumbs } from '@/components/admin';
+
+export const metadata: Metadata = {
+  title: {
+    template: '%s | Admin | FastNext Template',
+    default: 'Admin Dashboard',
+  },
+};
+
+export default function AdminLayout({ children }: { children: React.ReactNode }) {
+  return (
+    <AuthGuard requireAdmin>
+      <a
+        href="#main-content"
+        className="sr-only focus:not-sr-only focus:absolute focus:left-4 focus:top-4 focus:z-50 focus:rounded-md focus:bg-primary focus:px-4 focus:py-2 focus:text-primary-foreground focus:outline-none focus:ring-2 focus:ring-ring focus:ring-offset-2"
+      >
+        Skip to main content
+      </a>
+      <div className="flex min-h-screen flex-col">
+        <Header />
+        <div className="flex flex-1">
+          <AdminSidebar />
+          <div className="flex flex-1 flex-col">
+            <Breadcrumbs />
+            <main id="main-content" className="flex-1 overflow-y-auto">
+              {children}
+            </main>
+          </div>
+        </div>
+        <Footer />
+      </div>
+    </AuthGuard>
+  );
+}