feat(移动端): 确认页自动用券回显与优惠券模块显隐加固

computed 响应回传 coupon_id/coupon_title，引擎据此回显自动选中的优惠券；
优惠券模块显隐改为 features.coupon 或券标题非空双条件，confirm 请求带时间戳
防缓存，避免首次进入时模块隐藏而金额已含优惠的不一致。

frontend/uni-app/src/api/order-center.js

@@ -35,7 +35,8 @@ export function getCenterOrderDetail(orderNo) {
  * @param {Object} params { product_id, sku_unique, product_type, num }
  */
 export function getCenterOrderConfirm(params) {
-  return request.get('center/order/confirm', params);
+  // 携带时间戳避免浏览器缓存旧的确认数据（缓存会导致优惠券模块显隐/券列表陈旧）
+  return request.get('center/order/confirm', { ...params, _t: Date.now() });
 }
 
 /**

frontend/uni-app/src/dynamic-pages/components/order/create/OrderDiscountPanel.vue

@@ -4,8 +4,8 @@
 -->
 <template>
   <view class="wrapper">
-    <!-- 优惠券 -->
-    <view class="item acea-row row-between-wrapper" @tap="onCouponTap" v-if="features.coupon">
+    <!-- 优惠券（features.coupon 为后端开关；couponTitle 非空表示后端已自动选券，开关数据陈旧时也必须展示） -->
+    <view class="item acea-row row-between-wrapper" @tap="onCouponTap" v-if="features.coupon || couponTitle">
       <view>{{ $t('优惠券') }}</view>
       <view class="discount">
         {{ couponTitle || $t('请选择') }}

frontend/uni-app/src/dynamic-pages/engines/OrderCreateEngine.vue

@@ -603,6 +603,11 @@ async function computedPrice() {
     memberPrice.value = data.member_price ?? data.priceGroup?.memberPrice ?? memberPrice.value;
     postageDiscount.value = data.storePostageDiscount ?? data.postage_discount ?? data.priceGroup?.postageDiscount ?? postageDiscount.value;
     couponPrice.value = data.coupon_price ?? 0;
+    // 后端自动选券回显：未手动选券时展示后端自动领取并使用的优惠券
+    if (!couponId.value && data.coupon_id > 0) {
+      couponId.value = data.coupon_id;
+      couponTitle.value = data.coupon_title || i18n.global.t('请选择');
+    }
     integralPrice.value = data.deduction_price ?? 0;
     surplusIntegral.value = data.SurplusIntegral ?? usableIntegral.value;
     priceReady.value = true;