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/handler/admin/promo/getUsageListHandler.go

@@ -0,0 +1,23 @@
+package promo
+
+import (
+	"github.com/gin-gonic/gin"
+	"github.com/perfect-panel/server/internal/logic/admin/promo"
+	"github.com/perfect-panel/server/internal/svc"
+	"github.com/perfect-panel/server/internal/types"
+	"github.com/perfect-panel/server/pkg/result"
+)
+
+func GetUsageListHandler(svcCtx *svc.ServiceContext) func(c *gin.Context) {
+	return func(c *gin.Context) {
+		var req types.GetPromoUsageListRequest
+		_ = c.ShouldBind(&req)
+		if err := svcCtx.Validate(&req); err != nil {
+			result.ParamErrorResult(c, err)
+			return
+		}
+		l := promo.NewGetUsageListLogic(c.Request.Context(), svcCtx)
+		resp, err := l.GetUsageList(&req)
+		result.HttpResult(c, resp, err)
+	}
+}