fix(distribution): 修正商品归属回填、禁止全站灌货并拒绝无效站点头

用货架写入时间与上传来源回滚误标产地，不再依赖绝对时间戳；同步仅收本站上传与显式勾选。

backend/internal/modules/listing/presenter.go

@@ -18,7 +18,7 @@ type listingRow struct {
 	Title            string
 	OwnerPhone       string
 	OwnerNickname    string
-	SourceChannel        string `gorm:"column:source_channel"`
+	DisplaySourceChannel string `gorm:"column:display_source_channel"`
 	IsExternalUpload     bool   `gorm:"column:is_external_upload"`
 	DistributionSiteCode string `gorm:"column:distribution_site_code"`
 	DistributionSiteName string `gorm:"column:distribution_site_name"`
@@ -171,7 +171,7 @@ func (row listingRow) toDTO() ListingDTO {
 		OwnerID:           row.OwnerID,
 		OwnerPhone:        row.OwnerPhone,
 		OwnerNickname:     row.OwnerNickname,
-		SourceChannel:     row.SourceChannel,
+		SourceChannel:     row.DisplaySourceChannel,
 		IsExternalUpload:  row.IsExternalUpload,
 		Title:             row.Title,
 		Description:       row.Description,