feat: 新增退款管理模块 — 完整的退款审批流程、佣金回扣和资产重置

新增退款申请全生命周期管理：创建/列表/详情/审批通过/拒绝/退回/重新提交
审批通过后异步执行佣金全额回扣（扣减各代理佣金钱包）和资产重置（套餐失效+停机+世代重置）
新增 tb_refund_request 表（迁移 000093）、RefundRequest Model、8 个 DTO
新增 Store/Service/Handler/路由注册，仅平台用户可访问

internal/model/refund.go

@@ -0,0 +1,53 @@
+package model
+
+import (
+	"time"
+
+	"gorm.io/gorm"
+)
+
+// RefundRequest 退款申请模型
+// 记录退款申请的完整生命周期，包含退款单号、关联订单、金额、状态流转、审批信息等
+// 状态流转：1(待审批) → 2(已通过)/3(已拒绝)/4(已退回)，4(已退回) → 1(待审批)
+type RefundRequest struct {
+	gorm.Model
+	BaseModel `gorm:"embedded"`
+
+	// 退款单基础信息
+	RefundNo       string `gorm:"column:refund_no;type:varchar(50);uniqueIndex:idx_refund_request_refund_no,where:deleted_at IS NULL;not null;comment:退款单号（RF+日期时间+6位随机数）" json:"refund_no"`
+	OrderID        uint   `gorm:"column:order_id;index;not null;comment:关联订单ID" json:"order_id"`
+	PackageUsageID *uint  `gorm:"column:package_usage_id;comment:关联套餐使用记录ID（可选）" json:"package_usage_id,omitempty"`
+	ShopID         *uint  `gorm:"column:shop_id;index;comment:店铺ID（从订单获取，用于数据权限过滤）" json:"shop_id,omitempty"`
+
+	// 金额信息
+	ActualReceivedAmount  int64  `gorm:"column:actual_received_amount;type:bigint;not null;comment:实收金额（分）" json:"actual_received_amount"`
+	RequestedRefundAmount int64  `gorm:"column:requested_refund_amount;type:bigint;not null;comment:申请退款金额（分）" json:"requested_refund_amount"`
+	ApprovedRefundAmount  *int64 `gorm:"column:approved_refund_amount;type:bigint;comment:审批实际退款金额（分）" json:"approved_refund_amount,omitempty"`
+
+	// 退款原因和状态
+	RefundReason string `gorm:"column:refund_reason;type:text;comment:退款原因" json:"refund_reason"`
+	Status       int    `gorm:"column:status;type:int;not null;default:1;index;comment:状态 1-待审批 2-已通过 3-已拒绝 4-已退回" json:"status"`
+
+	// 审批信息
+	ProcessorID  *uint      `gorm:"column:processor_id;comment:审批人ID" json:"processor_id,omitempty"`
+	ProcessedAt  *time.Time `gorm:"column:processed_at;comment:审批时间" json:"processed_at,omitempty"`
+	RejectReason string     `gorm:"column:reject_reason;type:text;comment:拒绝原因" json:"reject_reason,omitempty"`
+	Remark       string     `gorm:"column:remark;type:text;comment:审批备注" json:"remark,omitempty"`
+
+	// 后处理标记
+	CommissionDeducted bool `gorm:"column:commission_deducted;not null;default:false;comment:佣金是否已回扣" json:"commission_deducted"`
+	AssetReset         bool `gorm:"column:asset_reset;not null;default:false;comment:资产是否已重置（套餐停用+停机+世代重置）" json:"asset_reset"`
+}
+
+// TableName 指定表名
+func (RefundRequest) TableName() string {
+	return "tb_refund_request"
+}
+
+// 退款状态常量
+const (
+	RefundStatusPending  = 1 // 待审批
+	RefundStatusApproved = 2 // 已通过
+	RefundStatusRejected = 3 // 已拒绝
+	RefundStatusReturned = 4 // 已退回
+)