新功能(#77): 套餐列表 API 返回规格级促销信息

将 promo 字段从 Subscribe 顶层移至 SubscribeDiscount（discount[] 项内），
促销查询按 subscribe_id + quantity 维度写入，每个规格独立命中最高优先级规则。

Co-authored-by: multica-agent <github@multica.ai>

internal/logic/public/subscribe/querySubscribeListLogic.go

@@ -56,11 +56,19 @@ func (l *QuerySubscribeListLogic) QuerySubscribeList(req *types.QuerySubscribeLi
 			var discount []types.SubscribeDiscount
 			_ = json.Unmarshal([]byte(item.Discount), &discount)
 			sub.Discount = discount
-			list[i] = sub
 		}
 		list[i] = sub
 	}
 
+	promos, err := loadSubscribePromoMap(l.ctx, l.svcCtx, subscribeIDs)
+	if err != nil {
+		l.Errorw("[QuerySubscribeListLogic] Query Promo Error", logger.Field("error", err.Error()))
+		return nil, err
+	}
+	for i := range list {
+		applySubscribeDiscountPromos(&list[i], promos[list[i].Id])
+	}
+
 	// 老版本客户端（无 X-App-Id）去掉每个套餐 discount 的最后一个
 	hasAppId, _ := l.ctx.Value(constant.CtxKeyHasAppId).(bool)
 	if !hasAppId {
@@ -71,16 +79,13 @@ func (l *QuerySubscribeListLogic) QuerySubscribeList(req *types.QuerySubscribeLi
 		}
 	}
 
-	promos, err := loadSubscribePromoMap(l.ctx, l.svcCtx, subscribeIDs)
-	if err != nil {
-		l.Errorw("[QuerySubscribeListLogic] Query Promo Error", logger.Field("error", err.Error()))
-		return nil, err
-	}
-	for i := range list {
-		list[i].Promo = promos[list[i].Id]
-	}
-
 	resp.List = list
 	resp.Total = int64(len(list))
 	return
 }
+
+func applySubscribeDiscountPromos(subscribe *types.Subscribe, promoByQuantity map[int64]*types.SubscribePromo) {
+	for i := range subscribe.Discount {
+		subscribe.Discount[i].Promo = promoByQuantity[subscribe.Discount[i].Quantity]
+	}
+}