- Add cn() utility function for class name merging
- Add Button component with default/outline/ghost variants
- Add Card component with Header, Title, Description, Content, Footer
- Add GoogleSignInButton with signInWithOAuth for Google provider
- Italian text: 'Accedi con Google'
- Redirects to /auth/callback after consent
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
