docs: explain dcim services and purchase flows

app/components/instance/DcimDomains.vue

@@ -1,4 +1,5 @@
 <script>
+// DCIM 域名白名单只读面板，先识别实例是否开通白名单，再按页读取关联记录。
 import "~/assets/styles/DcimDomains.BT2s5hGW.css";
 import { toDisplayString } from "vue";
 import { onMounted } from "vue";
@@ -53,6 +54,7 @@ var E = {
             F = ref(0),
             I = 0,
             L = !1;
+          // 页码控件从 0 开始，接口从 1 开始；实例切换或卸载后丢弃旧页面结果。
           async function R() {
             let e = ++I,
               t = y.hostId;