优化表结构，重构模型，重新实现基于白银网关的提取节点流程

web/models/refund.go

@@ -0,0 +1,26 @@
+package models
+
+import (
+	"platform/web/core"
+
+	"github.com/shopspring/decimal"
+)
+
+// Refund 退款记录表
+type Refund struct {
+	core.Model
+	TradeID   int32           `json:"trade_id" gorm:"column:trade_id"`     // 订单ID
+	ProductID *int32          `json:"product_id" gorm:"column:product_id"` // 产品ID
+	Amount    decimal.Decimal `json:"amount" gorm:"column:amount"`         // 退款金额
+	Reason    *string         `json:"reason" gorm:"column:reason"`         // 退款原因
+	Status    RefundStatus    `json:"status" gorm:"column:status"`         // 退款状态：0-待处理，1-已退款，2-已拒绝
+}
+
+// RefundStatus 退款状态枚举
+type RefundStatus int
+
+const (
+	RefundStatusPending  RefundStatus = 0 // 待处理
+	RefundStatusRefunded RefundStatus = 1 // 已退款
+	RefundStatusRejected RefundStatus = 2 // 已拒绝
+)