fix(devfront): add explicit button type and improve test stability

devfront/src/features/auth/AuthGuard.tsx

@@ -16,6 +16,7 @@ export default function AuthGuard() {
           <p>{auth.error.message}</p>
         </div>
         <button
+          type="button"
           onClick={() => void auth.signinRedirect()}
           className="rounded bg-blue-500 px-4 py-2 text-white hover:bg-blue-600"
         >