Show login progress immediately and stop auth 401 hangs.

Co-authored-by: Cursor <cursoragent@cursor.com>

interfaces/admin/static/js/chat/i18n/messages-en.js

@@ -4,6 +4,7 @@ export default {
   "auth.disabled": "Account is disabled",
   "auth.invalid": "Login failed",
   "auth.login": "Login",
+  "auth.loggingIn": "Signing in…",
   "auth.logout": "Logout",
   "auth.password": "Password",
   "auth.username": "Username",

interfaces/admin/static/js/chat/i18n/messages-zh.js

@@ -4,6 +4,7 @@ export default {
   "auth.disabled": "账号已被禁用，请联系管理员",
   "auth.invalid": "登录失败，请检查凭据",
   "auth.login": "登录",
+  "auth.loggingIn": "登录中…",
   "auth.logout": "退出登录",
   "auth.password": "密码",
   "auth.username": "用户名",