fix: 修复登录失败提示不准确的问题

- 后端：手机号不存在时返回用户名或密码错误，避免 NPE 导致系统繁忙提示
- 前端：兼容后端 message 字段名，避免双重 Toast 提示

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

admin-h5/src/pages/login/login.vue

@@ -143,7 +143,10 @@ const handleLogin = async () => {
     }
   } catch (error) {
     console.error('登录失败:', error)
-    showToast(error.msg || error.message || '网络错误，请稍后重试')
+    // 业务错误已被 request 拦截器提示，仅网络异常时补充提示
+    if (!error.msg && !error.message) {
+      showToast('网络错误，请稍后重试')
+    }
   } finally {
     loading.value = false
   }

car-wash-service/src/main/java/com/kym/service/impl/AdminUserServiceImpl.java

@@ -90,6 +90,9 @@ public class AdminUserServiceImpl extends MyBaseServiceImpl<AdminUserMapper, Adm
     @Override
     public R<?> login(String mobilePhone, String password) {
         var user = lambdaQuery().eq(AdminUser::getMobilePhone, mobilePhone).one();
+        if (user == null) {
+            return R.failed(ResponseEnum.LOGIN_FAILED);
+        }
         if (user.getStatus() == AdminUser.STATUS_禁用) {
             throw new BusinessException("用户状态异常，无法登录");
         }