fix(distribution): 货架加价打通前台、下单与卖方分成

分站公开列表和详情展示当前货架加价；下单写入 base_price / shelf_markup / markup_site_id 快照并计入实付。
支付分账改用快照加价，不再误用 PlatformFeeCent；结账不退加价，事后改价不影响历史订单。

backend/internal/modules/distribution/lifecycle.go

@@ -186,7 +186,10 @@ func SnapshotPaidOrderTx(tx *gorm.DB, orderID uint64, grossPaidCent int64) error
 	if err := tx.First(&rule, *order.DistributionRuleVersionID).Error; err != nil {
 		return err
 	}
-	markup := order.PlatformFeeCent
+	markup := order.ShelfMarkupCent
+	if markup < 0 {
+		markup = 0
+	}
 	result, err := calculateForRule(rule, SettlementInput{GrossPaidAmountCent: grossPaidCent, MarkupAmountCent: markup})
 	if err != nil {
 		return err

backend/internal/modules/distribution/lifecycle_test.go

@@ -279,7 +279,8 @@ func TestSnapshotPaidOrderTxAndApplyRefundTx(t *testing.T) {
 		OwnerID:                   1,
 		RenterID:                  2,
 		Status:                    "renting",
-		PlatformFeeCent:           300,
+		PlatformFeeCent:           999,
+		ShelfMarkupCent:           300,
 		DistributionSiteID:        &site.ID,
 		DistributionRuleVersionID: &rule.ID,
 	}
@@ -300,6 +301,9 @@ func TestSnapshotPaidOrderTxAndApplyRefundTx(t *testing.T) {
 	if financial.GrossPaidAmountCent != grossPaid || financial.SiteID != site.ID {
 		t.Fatalf("unexpected financial snapshot: %+v", financial)
 	}
+	if financial.MarkupAmountCent != 300 {
+		t.Fatalf("markup must come from shelf snapshot, got %d", financial.MarkupAmountCent)
+	}
 
 	var parties []model.DistributionOrderParty
 	if err := db.Where("order_id = ?", order.ID).Order("id ASC").Find(&parties).Error; err != nil || len(parties) != 2 {
@@ -347,3 +351,64 @@ func TestSnapshotPaidOrderTxAndApplyRefundTx(t *testing.T) {
 		t.Fatalf("expected net paid %d, got %d", grossPaid-refundAmount, updatedFinancial.NetPaidAmountCent)
 	}
 }
+
+func TestSnapshotPaidOrderTxAddsShelfMarkupToSeller(t *testing.T) {
+	db := distributionTestDB(t)
+	now := time.Now()
+	site := model.DistributionSite{SiteCode: "sell_markup", SiteName: "卖出加价站", Domain: "sell-markup.dist.com", Status: "active", DisplayAccountEnabled: true}
+	if err := db.Create(&site).Error; err != nil {
+		t.Fatal(err)
+	}
+	rule := model.DistributionRuleVersion{
+		SiteID: &site.ID, Mode: ModeTwoPartyPlatformReceive, Version: 1, Status: "active",
+		PlatformReceiveRatio: 3.5, DistributorSellRatio: 4,
+		ServiceFeeValue: 0, ServiceFeeUnit: ServiceFeeUnitFixedAmount, PaymentFeeBPS: 50,
+		EffectiveFrom: now.Add(-time.Hour),
+	}
+	if err := db.Create(&rule).Error; err != nil {
+		t.Fatal(err)
+	}
+	order := model.RentalOrder{
+		OrderNo: "ORD-MARKUP-SELL", ListingID: 1, AccountID: 2, OwnerID: 3, RenterID: 4, Status: "renting",
+		PlatformFeeCent: 2000, ShelfMarkupCent: 10000,
+		DistributionSiteID: &site.ID, DistributionRuleVersionID: &rule.ID, DistributionMode: ModeTwoPartyPlatformReceive,
+	}
+	if err := db.Create(&order).Error; err != nil {
+		t.Fatal(err)
+	}
+	if err := SnapshotPaidOrderTx(db, order.ID, 20000); err != nil {
+		t.Fatal(err)
+	}
+	var parties []model.DistributionOrderParty
+	if err := db.Where("order_id = ?", order.ID).Find(&parties).Error; err != nil {
+		t.Fatal(err)
+	}
+	var seller, platform *model.DistributionOrderParty
+	for i := range parties {
+		switch parties[i].PartyRole {
+		case "distributor_sell":
+			seller = &parties[i]
+		case "platform_receive":
+			platform = &parties[i]
+		}
+	}
+	if seller == nil || platform == nil {
+		t.Fatalf("missing parties: %+v", parties)
+	}
+	if seller.IncomeAmountCent < 10000 {
+		t.Fatalf("seller split must include 10000 markup, got %d", seller.IncomeAmountCent)
+	}
+	if platform.PartyID != 0 {
+		t.Fatalf("platform party_id = %d, want 0", platform.PartyID)
+	}
+	if err := db.Model(&order).Update("shelf_markup_cent", 0).Error; err != nil {
+		t.Fatal(err)
+	}
+	var financial model.DistributionOrderFinancial
+	if err := db.Where("order_id = ?", order.ID).First(&financial).Error; err != nil {
+		t.Fatal(err)
+	}
+	if financial.MarkupAmountCent != 10000 {
+		t.Fatalf("historical snapshot must keep markup, got %d", financial.MarkupAmountCent)
+	}
+}