feat(mhzc): 新增getCaptcha API

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

txw-mhzc-web/src/pages/index/api/login.js

@@ -129,6 +129,14 @@ export function Getqrcode() {
     method: 'post',
   });
 }
+
+// 获取图形验证码
+export function getCaptcha() {
+  return fetchSso({
+    url: `${basurl}/sso/verify/captcha`,
+    method: 'post',
+  });
+}
 //获取登录回调响应结果
 export function backresultlogin(params) {
   return fetchSso({