feat(auth): add google sign-in onboarding flow

src/pages/Auth.tsx

@@ -6,7 +6,7 @@ import { SettingsMenu } from "../components/SettingsMenu"
 import { AlertTriangle, ArrowLeft, ArrowRight, Command, Eye, EyeOff, Loader2 } from "lucide-react"
 import { toast } from "sonner"
 import { useTranslation } from "../hooks/useTranslation"
-import { loginWithOtp, loginWithPassword, sendOtp } from "../api/users"
+import { loginWithOtp, loginWithPassword, sendOtp, startGoogleLogin } from "../api/users"
 import { ApiError } from "../api/client"
 import { setSessionTokens } from "../lib/session"
 
@@ -299,6 +299,16 @@ export default function Auth() {
                   </div>
                 </div>
 
+                <Button
+                  type="button"
+                  variant="outline"
+                  onClick={startGoogleLogin}
+                  disabled={loading}
+                  className="h-11 w-full"
+                >
+                  {t.login.continueWithGoogle}
+                </Button>
+
                 <div className="grid grid-cols-2 gap-4">
                   <Button
                     variant="outline"