feat(01-04): add Google button to login and register pages

- Add auth layout with centered card design
- Add Input component for form fields
- Add LoginForm component with email/password and validation
- Add RegisterForm component with password requirements
- Add login page with Google button + 'oppure' divider + email form
- Add register page with Google button + 'oppure' divider + email form
- Italian text throughout (Accedi, Registrati, oppure)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/app/(auth)/login/page.tsx

@@ -0,0 +1,30 @@
+import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card'
+import { LoginForm } from '@/components/auth/login-form'
+import { GoogleSignInButton } from '@/components/auth/google-button'
+
+export default function LoginPage() {
+  return (
+    <Card>
+      <CardHeader className="text-center">
+        <CardTitle>Accedi a Leopost</CardTitle>
+        <CardDescription>
+          Inserisci le tue credenziali per continuare
+        </CardDescription>
+      </CardHeader>
+      <CardContent className="space-y-4">
+        <GoogleSignInButton />
+
+        <div className="relative">
+          <div className="absolute inset-0 flex items-center">
+            <span className="w-full border-t border-gray-300" />
+          </div>
+          <div className="relative flex justify-center text-xs uppercase">
+            <span className="bg-white px-2 text-gray-500">oppure</span>
+          </div>
+        </div>
+
+        <LoginForm />
+      </CardContent>
+    </Card>
+  )
+}