fix(buyer): 未登录联系客服时提示登录

- 将登录提示由 Message 改为 Modal
- 新增 promptLogin 方法处理登录跳转
- IMService 增加 accessToken 校验，未登录时提示登录
- 改进用户信息获取的错误处理
- 重构 IM 链接 URL 拼接，提升可读性

buyer/src/pages/home/orderCenter/AfterSale.vue

@@ -198,7 +198,7 @@ export default {
     // 跳转店铺首页
     shopPage(id) {
       let routeUrl = this.$router.resolve({
-        path: '/Merchant',
+        path: '/merchant',
         query: {id: id}
       });
       window.open(routeUrl.href, '_blank');

buyer/src/pages/home/orderCenter/MyOrder.vue

@@ -265,7 +265,7 @@ export default {
     // 跳转店铺首页
     shopPage (id) {
       let routeUrl = this.$router.resolve({
-        path: '/Merchant',
+        path: '/merchant',
         query: { id: id }
       });
       window.open(routeUrl.href, '_blank');

buyer/src/pages/home/orderCenter/OrderDetail.vue

@@ -424,7 +424,7 @@ export default {
     // 跳转店铺首页
     shopPage(id) {
       let routeUrl = this.$router.resolve({
-        path: "/Merchant",
+        path: "/merchant",
         query: { id: id },
       });
       window.open(routeUrl.href, "_blank");