docs: explain stylesheet ownership, responsive rules and display boundaries

app/assets/styles/PromoCodeField.qFEkB6Hm.css

@@ -1,3 +1,5 @@
+/* 优惠码输入：输入/操作区及校验说明。 */
+/* 导入方：app/components/config/CommonConfig.vue、app/components/config/ConfigCheckout.vue、app/components/config/FinanceConfig.vue、app/components/config/JyCloudConfig.vue、app/components/config/KkyEcsConfig.vue、app/components/config/MfCloudConfig.vue、app/components/config/MfDcimConfig.vue、app/components/config/PromoCodeField.vue、app/pages/products/[id].vue、app/pages/products/cloud-server.vue、app/pages/products/dedicated-server/customize.vue。 */
 .promo summary[data-v-a17e621a] {
   color: var(--p-primary-color);
   cursor: pointer;