feat(distribution): 分站收号压价解耦买家价（方案 B 新口径）

核心语义反转：receive_cost_delta 为压价点数，收号比例 = 主站参考比例 R + 点数，
点数越大号主收号价越低；买家售价锚定主站参考比例推导，不再随收号价联动。

- 迁移 000072：distribution_sites 新增 receive_cost_delta（旧 receive_ratio_delta 保留只读）
- receive_pricing：新增 Normalize/ApplySiteReceiveCostDelta；分站定价买家侧改用
  R 锚点（referenceSellerCoinBasePrice），快照写入 site_receive_cost_delta 与 pricing_model 标记
- site_receive：新增 resolveSiteReceiveCostDelta 读取链路，旧 ResolveReceiveRatioDelta 保留
- 分成不变：压价差经结算层 profit 自动进入 35/40/25 三方分成池；
  货架自主加价仍 100% 归分站，两条边界均以主站为锚
- 权限对齐旧字段：主站全局管理员与分站操作员均可设置
- 前端三端同步：主站 pricing.ts/usePricingCalculator 买卖解耦试算、
  主站后台弹窗改「收号压价」价格语义文案、分销后台 SiteSettings 同步
- 测试：单测锚定 R=43 时 cost_delta=3 → 收号 217.4 / 卖价 263.2 不变 / markup 池 30.6→54.9

backend/internal/modules/distribution/dto.go

@@ -17,6 +17,7 @@ type SiteDTO struct {
 	DefaultSupportGroupID *uint64   `json:"default_support_group_id,omitempty"`
 	ListingQrcodeURL      string    `json:"listing_qrcode_url"`
 	ReceiveRatioDelta     float64   `json:"receive_ratio_delta"`
+	ReceiveCostDelta      float64   `json:"receive_cost_delta"`
 	TaxEnabled            bool      `json:"tax_enabled"`
 	TaxRateBPS            int64     `json:"tax_rate_bps"`
 	SettlementHoldDays    int       `json:"settlement_hold_days"`
@@ -32,6 +33,7 @@ type CreateSiteRequest struct {
 	DefaultSupportGroupID *uint64  `json:"default_support_group_id"`
 	ListingQrcodeURL      *string  `json:"listing_qrcode_url"`
 	ReceiveRatioDelta     *float64 `json:"receive_ratio_delta"`
+	ReceiveCostDelta      *float64 `json:"receive_cost_delta"`
 	TaxEnabled            *bool    `json:"tax_enabled"`
 	TaxRateBPS            *int64   `json:"tax_rate_bps"`
 	SettlementHoldDays    *int     `json:"settlement_hold_days"`
@@ -45,6 +47,7 @@ type UpdateSiteRequest struct {
 	DefaultSupportGroupID *uint64  `json:"default_support_group_id"`
 	ListingQrcodeURL      *string  `json:"listing_qrcode_url"`
 	ReceiveRatioDelta     *float64 `json:"receive_ratio_delta"`
+	ReceiveCostDelta      *float64 `json:"receive_cost_delta"`
 	TaxEnabled            *bool    `json:"tax_enabled"`
 	TaxRateBPS            *int64   `json:"tax_rate_bps"`
 	SettlementHoldDays    *int     `json:"settlement_hold_days"`
@@ -248,6 +251,7 @@ type PublicSiteInfoDTO struct {
 	FooterInfoJSON        string  `json:"footer_info_json"`
 	DefaultSupportGroupID *uint64 `json:"default_support_group_id,omitempty"`
 	ReceiveRatioDelta     float64 `json:"receive_ratio_delta"`
+	ReceiveCostDelta      float64 `json:"receive_cost_delta"`
 }
 
 type UpdateAccountDisplayRequest struct {

backend/internal/modules/distribution/repository.go

@@ -73,6 +73,13 @@ func normalizeReceiveRatioDelta(delta float64) (float64, error) {
 	return listingpkg.NormalizeSiteReceiveRatioDelta(delta), nil
 }
 
+func normalizeReceiveCostDelta(delta float64) (float64, error) {
+	if delta < 0 {
+		return 0, ErrInvalidAmount
+	}
+	return listingpkg.NormalizeSiteReceiveCostDelta(delta), nil
+}
+
 type Repository struct {
 	db            *gorm.DB
 	redis         *redis.Client
@@ -333,6 +340,13 @@ func (r *Repository) CreateSite(ctx context.Context, req CreateSiteRequest) (*Si
 		}
 		row.ReceiveRatioDelta = delta
 	}
+	if req.ReceiveCostDelta != nil {
+		delta, err := normalizeReceiveCostDelta(*req.ReceiveCostDelta)
+		if err != nil {
+			return nil, err
+		}
+		row.ReceiveCostDelta = delta
+	}
 	if req.TaxEnabled != nil {
 		row.TaxEnabled = *req.TaxEnabled
 	}
@@ -385,6 +399,13 @@ func (r *Repository) UpdateSite(ctx context.Context, adminID, id uint64, req Upd
 			}
 			row.ReceiveRatioDelta = delta
 		}
+		if req.ReceiveCostDelta != nil {
+			delta, err := normalizeReceiveCostDelta(*req.ReceiveCostDelta)
+			if err != nil {
+				return err
+			}
+			row.ReceiveCostDelta = delta
+		}
 		if !globalAccess {
 			if err := tx.Save(&row).Error; err != nil {
 				return err
@@ -573,6 +594,7 @@ func siteDTO(row model.DistributionSite) SiteDTO {
 		DefaultSupportGroupID: row.DefaultSupportGroupID,
 		ListingQrcodeURL:      row.ListingQrcodeURL,
 		ReceiveRatioDelta:     row.ReceiveRatioDelta,
+		ReceiveCostDelta:      row.ReceiveCostDelta,
 		TaxEnabled:            row.TaxEnabled,
 		TaxRateBPS:            row.TaxRateBPS,
 		SettlementHoldDays:    row.SettlementHoldDays,
@@ -2330,6 +2352,7 @@ func (r *Repository) GetPublicSiteInfo(ctx context.Context, code, domain string)
 		AnnouncementsJSON:     site.AnnouncementsJSON,
 		FooterInfoJSON:        site.FooterInfoJSON,
 		ReceiveRatioDelta:     site.ReceiveRatioDelta,
+		ReceiveCostDelta:      site.ReceiveCostDelta,
 	}
 	if r.redis != nil {
 		if bytes, err := json.Marshal(res); err == nil {