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/listing/service_test.go

@@ -1116,7 +1116,7 @@ func TestCreateDistributionListingUsesMainSiteReceiveRatio(t *testing.T) {
 	}
 }
 
-func TestCreateDistributionListingAppliesSiteReceiveRatioDelta(t *testing.T) {
+func TestCreateDistributionListingAppliesSiteReceiveCostDelta(t *testing.T) {
 	db := database.NewTestDB()
 	if err := database.MigrateListingLifecycleTestSchema(db); err != nil {
 		t.Fatalf("migrate err: %v", err)
@@ -1129,11 +1129,11 @@ func TestCreateDistributionListingAppliesSiteReceiveRatioDelta(t *testing.T) {
 	}
 	site := model.DistributionSite{
 		SiteCode:              "dist_ratio_down",
-		SiteName:              "下调收号站",
+		SiteName:              "压价收号站",
 		Domain:                "ratio-down.example.com",
 		Status:                "active",
 		DisplayAccountEnabled: true,
-		ReceiveRatioDelta:     3,
+		ReceiveCostDelta:      3,
 	}
 	if err := db.Create(&site).Error; err != nil {
 		t.Fatal(err)
@@ -1169,8 +1169,8 @@ func TestCreateDistributionListingAppliesSiteReceiveRatioDelta(t *testing.T) {
 		t.Fatalf("Create failed: %v", err)
 	}
 	pricing := ReceivePricingFromAssetSummary(mustMarshalSummary(t, dto.AssetSummary))
-	if pricing.SellerRatio != 40 {
-		t.Fatalf("seller_ratio = %v, want 40 after site delta 3 below main-site 43", pricing.SellerRatio)
+	if pricing.SellerRatio != 46 {
+		t.Fatalf("seller_ratio = %v, want 46 after site cost delta 3 (R=43+3) under decoupled model", pricing.SellerRatio)
 	}
 }