Add and enhance tests for mobile navigation, demo modal, and forbidden page metadata

- Added new test cases for mobile navigation links and buttons in `Header` component.
- Enhanced `Home` tests to verify demo modal behavior (open/close functionality).
- Added metadata validation test for the forbidden page.
- Introduced comprehensive test suite for the DemoTour page, covering structure, navigation, categories, accessibility, and CTAs.

frontend/src/app/forbidden/page.tsx

@@ -9,8 +9,7 @@ import Link from 'next/link';
 import { ShieldAlert } from 'lucide-react';
 import { Button } from '@/components/ui/button';
 
-/* istanbul ignore next - Next.js metadata, not executable code */
-export const metadata: Metadata = {
+export const metadata: Metadata = /* istanbul ignore next */ {
   title: '403 - Forbidden',
   description: 'You do not have permission to access this resource',
 };