feat(distribution): 补齐退款加价回退、本站自卖与开通默认规则

退款时压缩卖方加价，人工/自动批次仅完结单可入账，号主收入进主站钱包；仲裁后重算释放并支持作废未入账 DS。开通时四种模式按默认生效，对外口径合并为 35/40/25，不再单独展示通道费。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/internal/modules/distribution/handler.go

@@ -440,6 +440,20 @@ func (h *Handler) MarkSettlementBatch(c *gin.Context) {
 	response.OK(c, item)
 }
 
+func (h *Handler) CancelSettlementBatch(c *gin.Context) {
+	id, ok := parseID(c)
+	if !ok {
+		return
+	}
+	adminID, _ := currentAdminID(c)
+	item, err := h.service.CancelSettlementBatch(c.Request.Context(), adminID, id)
+	if err != nil {
+		writeError(c, err)
+		return
+	}
+	response.OK(c, item)
+}
+
 // parseQueryUint 返回 -1 表示格式错误，0 表示未传入。
 func parseQueryUint(c *gin.Context, key string) int64 {
 	raw := strings.TrimSpace(c.Query(key))
@@ -761,6 +775,10 @@ func writeError(c *gin.Context, err error) {
 		response.Error(c, http.StatusForbidden, "admin_disabled", "分销管理员账号已被禁用")
 	case errors.Is(err, ErrInvalidAmount), errors.Is(err, ErrInvalidRate), errors.Is(err, ErrInvalidServiceUnit), errors.Is(err, ErrUnsupportedMode), errors.Is(err, ErrInvalidOrderKind), errors.Is(err, ErrInvalidPeriod), errors.Is(err, ErrBatchAlreadySettled), errors.Is(err, ErrSettlementBatchEmpty), errors.Is(err, ErrSettlementTotalMismatch):
 		response.BadRequest(c, "分销规则参数不正确")
+	case errors.Is(err, ErrInvalidSettlementHold):
+		response.BadRequest(c, "结算冷却天数须在 0 到 365 之间")
+	case errors.Is(err, ErrBatchNotCancellable):
+		response.BadRequest(c, "该结算批次无法作废")
 	case errors.Is(err, ErrTooManySyncListings):
 		response.BadRequest(c, "一次勾选同步的商品过多")
 	case errors.Is(err, ErrSyncListingNotFound):