修复(#79): 促销管理后台API + 审查问题修复

- 实现促销管理接口：规则CRUD、优惠价配置、使用记录查询
- 修复 UpsertPrices 新增记录时提前 return 的问题
- DeleteRule/DeletePrice 不存在记录返回 code=404
- SetPromoPriceRequest.items 空数组校验
- 分页参数限制 page>0、1<=size<=200
- 下单侧促销价格按数量档总价口径计算（含 #87 修复）

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

internal/logic/admin/promo/getPriceListLogic.go

@@ -0,0 +1,41 @@
+package promo
+
+import (
+	"context"
+
+	"github.com/perfect-panel/server/internal/svc"
+	"github.com/perfect-panel/server/internal/types"
+	"github.com/perfect-panel/server/pkg/logger"
+	"github.com/perfect-panel/server/pkg/xerr"
+	"github.com/pkg/errors"
+)
+
+type GetPriceListLogic struct {
+	logger.Logger
+	ctx    context.Context
+	svcCtx *svc.ServiceContext
+}
+
+func NewGetPriceListLogic(ctx context.Context, svcCtx *svc.ServiceContext) *GetPriceListLogic {
+	return &GetPriceListLogic{
+		Logger: logger.WithContext(ctx),
+		ctx:    ctx,
+		svcCtx: svcCtx,
+	}
+}
+
+func (l *GetPriceListLogic) GetPriceList(req *types.GetPromoPriceListRequest) (*types.GetPromoPriceListResponse, error) {
+	total, list, err := l.svcCtx.PromoModel.QueryPriceList(l.ctx, req.PromoRuleId, int(req.Page), int(req.Size))
+	if err != nil {
+		l.Errorw("[GetPromoPriceList] Database Error", logger.Field("error", err.Error()))
+		return nil, errors.Wrapf(xerr.NewErrCode(xerr.DatabaseQueryError), "get promo price list error: %v", err.Error())
+	}
+	resp := &types.GetPromoPriceListResponse{
+		Total: total,
+		List:  make([]types.PromoPrice, 0, len(list)),
+	}
+	for _, item := range list {
+		resp.List = append(resp.List, convertPrice(item))
+	}
+	return resp, nil
+}