feat(marketing): add contact form submission and testing setup

- Add contact API endpoint for demo requests and sales enquiries
- Implement functional contact forms on Demo and Pricing pages with honeypot spam protection
- Update footer layout: remove Company section, add contact email
- Update self-hosted FAQ to mention open source with GitHub links
- Add vitest and testing-library dependencies
- Add tests for MarketingLayout and PricingPage components
- Remove placeholder external-auth test file

tests/PricingPage.test.tsx

@@ -0,0 +1,22 @@
+import { render, screen } from '@testing-library/react';
+import PricingPage from '../src/pages/marketing/PricingPage';
+import { expect, test, describe } from 'bun:test';
+
+describe('PricingPage', () => {
+  test('Self-hosted FAQ answer updated to mention open source with GitHub links', () => {
+    render(<PricingPage />);
+    const selfHostedText = screen.getByText(/self-hosted/i);
+    expect(selfHostedText).toBeDefined();
+
+    const openSourceText = screen.getByText(/open source/i);
+    expect(openSourceText).toBeDefined();
+
+    const gatehouseUiLink = screen.getByRole('link', { name: 'gatehouse-ui' });
+    expect(gatehouseUiLink).toBeDefined();
+    expect(gatehouseUiLink).toHaveAttribute('href', 'https://github.com/gatehouse/gatehouse-ui');
+
+    const gatehouseApiLink = screen.getByRole('link', { name: 'gatehouse-api' });
+    expect(gatehouseApiLink).toBeDefined();
+    expect(gatehouseApiLink).toHaveAttribute('href', 'https://github.com/gatehouse/gatehouse-api');
+  });
+});