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]/(authenticated)/layout.tsx

@@ -0,0 +1,28 @@
+/**
+ * Authenticated Route Group Layout
+ * Wraps all authenticated routes with AuthGuard and provides common layout structure
+ */
+
+import type { Metadata } from 'next';
+import { AuthGuard } from '@/components/auth';
+import { Header } from '@/components/layout/Header';
+import { Footer } from '@/components/layout/Footer';
+
+export const metadata: Metadata = {
+  title: {
+    template: '%s | FastNext Template',
+    default: 'Dashboard',
+  },
+};
+
+export default function AuthenticatedLayout({ children }: { children: React.ReactNode }) {
+  return (
+    <AuthGuard>
+      <div className="flex min-h-screen flex-col">
+        <Header />
+        <main className="flex-1">{children}</main>
+        <Footer />
+      </div>
+    </AuthGuard>
+  );
+}