fix(auth): fix NameError in logout endpoint - sso_login used before assignment

The logout handler referenced `sso_login` before it was defined, causing
a 500 Internal Server Error when users tried to log out.

gpustack/routes/auth.py

@@ -554,11 +554,11 @@ async def logout(request: Request):
             external_logout_url = None
 
     # SSO logout: return SSO platform logout URL
+    sso_login = request.cookies.get(SSO_LOGIN_COOKIE_NAME)
     sso_logout_url = config.sso_logout_redirect_url
     if sso_login and sso_logout_url:
         external_logout_url = sso_logout_url
 
-    sso_login = request.cookies.get(SSO_LOGIN_COOKIE_NAME)
     content = json.dumps({"logout_url": external_logout_url}) if sso_login else ""
     resp = Response(content=content, media_type="application/json")
     resp.delete_cookie(key=SESSION_COOKIE_NAME)