重构: 手续费改为百分比/固定二选一，清理旧 Skin/Order/ShipLog 演示链路

手续费:
- 新增 fee_type 字段(rate/fixed)，百分比与固定金额二选一，不再叠加
- calculateServiceFee 按 fee_type 分支计算
- 商户创建/更新校验 fee_type，订单落库快照 fee_type
- 前端表单改为下拉选择手续费类型，动态显示对应输入框
- 测试拆为 TestFeeRate + TestFeeFixed

清理旧链路:
- 删除旧 Skin/Order/ShipLog 模型及 OrderService/SkinService
- Dashboard 迁移到 FulfillmentService
- 上游 /api/open/v1 改为基于 FulfillmentOrder 实现，接口契约不变
- 推送留痕改用 AuditLog，不再建 ShipLog 表
- 删除前端 Skins/Orders/ShipLogs/Distributors 页面及路由、菜单、API、类型
- 新增迁移 003: 添加 fee_type 列并 DROP 旧表

backend/internal/model/merchant.go

@@ -10,11 +10,21 @@ const (
 	MerchantStatusActive   = "active"
 	MerchantStatusDisabled = "disabled"
 
+	MerchantFeatureProducts  = "products"
+	MerchantFeatureOrders    = "orders"
+	MerchantFeatureWallet    = "wallet"
+	MerchantFeatureAPI       = "api"
+	MerchantFeatureCallbacks = "callbacks"
+	DefaultMerchantFeatures  = "products,orders,wallet,api,callbacks"
+
 	MemberRoleOwner    = "owner"
 	MemberRoleOperator = "operator"
 	MemberRoleFinance  = "finance"
 	MemberRoleViewer   = "viewer"
 
+	FeeTypeRate  = "rate"  // 手续费按百分比
+	FeeTypeFixed = "fixed" // 手续费按固定金额
+
 	APIClientStatusActive   = "active"
 	APIClientStatusDisabled = "disabled"
 
@@ -63,6 +73,22 @@ type Merchant struct {
 	Status      string `gorm:"size:16;not null;default:active;index" json:"status"`
 	ContactName string `gorm:"size:64" json:"contact_name"`
 	ContactInfo string `gorm:"size:128" json:"contact_info"`
+	Features    string `gorm:"type:text;not null;default:'products,orders,wallet,api,callbacks'" json:"features"`
+
+	// 手续费按"百分比或固定"二选一：fee_type=rate 用 fee_rate_bp，fee_type=fixed 用 fee_fixed_amount。
+	FeeType        string `gorm:"size:16;not null;default:rate" json:"fee_type"`
+	FeeRateBP      int64  `gorm:"not null;default:0" json:"fee_rate_bp"`
+	FeeFixedAmount int64  `gorm:"not null;default:0" json:"fee_fixed_amount"`
+}
+
+func (m *Merchant) BeforeCreate(tx *gorm.DB) error {
+	if m.Features == "" {
+		m.Features = DefaultMerchantFeatures
+	}
+	if m.FeeType == "" {
+		m.FeeType = FeeTypeRate
+	}
+	return nil
 }
 
 // MerchantMember 将系统账号和商户权限分离，账号可以属于多个商户。
@@ -179,6 +205,11 @@ type FulfillmentOrder struct {
 	ProductSKU        string     `gorm:"size:96;not null" json:"product_sku"`
 	ProductName       string     `gorm:"size:160;not null" json:"product_name"`
 	Quantity          int64      `gorm:"not null;default:1" json:"quantity"`
+	BaseAmount        int64      `gorm:"not null;default:0" json:"base_amount"`
+	FeeType           string     `gorm:"size:16;not null;default:rate" json:"fee_type"`
+	FeeRateBP         int64      `gorm:"not null;default:0" json:"fee_rate_bp"`
+	FeeFixedAmount    int64      `gorm:"not null;default:0" json:"fee_fixed_amount"`
+	ServiceFeeAmount  int64      `gorm:"not null;default:0" json:"service_fee_amount"`
 	Amount            int64      `gorm:"not null" json:"amount"`
 	Currency          string     `gorm:"size:12;not null;default:CNY" json:"currency"`
 	PaymentStatus     string     `gorm:"size:16;not null;default:pending;index" json:"payment_status"`