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/dto/refund_dto.go

@@ -0,0 +1,84 @@
+package dto
+
+// CreateRefundRequest 创建退款申请请求
+type CreateRefundRequest struct {
+	OrderID               uint   `json:"order_id" validate:"required" required:"true" description:"关联订单ID"`
+	ActualReceivedAmount  int64  `json:"actual_received_amount" validate:"required,min=1" required:"true" minimum:"1" description:"实收金额（分）"`
+	RequestedRefundAmount int64  `json:"requested_refund_amount" validate:"required,min=1" required:"true" minimum:"1" description:"申请退款金额（分）"`
+	RefundReason          string `json:"refund_reason" validate:"omitempty,max=1000" maxLength:"1000" description:"退款原因"`
+	PackageUsageID        *uint  `json:"package_usage_id" validate:"omitempty" description:"关联套餐使用记录ID（可选）"`
+}
+
+// RefundIDRequest 退款申请ID路径参数
+type RefundIDRequest struct {
+	ID uint `path:"id" description:"退款申请ID" required:"true"`
+}
+
+// RejectRefundRequest 拒绝退款申请请求
+type RejectRefundRequest struct {
+	ID           uint   `json:"-" params:"id" path:"id" validate:"required" description:"退款申请ID"`
+	RejectReason string `json:"reject_reason" validate:"required,max=500" required:"true" maxLength:"500" description:"拒绝原因（必填）"`
+}
+
+// ResubmitRefundRequest 重新提交退款申请请求
+// 退款单被退回后，可修改部分字段后重新提交
+type ResubmitRefundRequest struct {
+	ID                    uint    `json:"-" params:"id" path:"id" validate:"required" description:"退款申请ID"`
+	ActualReceivedAmount  *int64  `json:"actual_received_amount" validate:"omitempty,min=1" minimum:"1" description:"实收金额（分）"`
+	RequestedRefundAmount *int64  `json:"requested_refund_amount" validate:"omitempty,min=1" minimum:"1" description:"申请退款金额（分）"`
+	RefundReason          *string `json:"refund_reason" validate:"omitempty,max=1000" maxLength:"1000" description:"退款原因"`
+}
+
+// ApproveRefundRequest 审批通过退款申请请求
+type ApproveRefundRequest struct {
+	ID                   uint   `json:"-" params:"id" path:"id" validate:"required" description:"退款申请ID"`
+	ApprovedRefundAmount *int64 `json:"approved_refund_amount" validate:"omitempty,min=1" minimum:"1" description:"审批实际退款金额（分），不填则使用申请金额"`
+	Remark               string `json:"remark" validate:"omitempty,max=500" maxLength:"500" description:"审批备注"`
+}
+
+// ReturnRefundRequest 退回退款申请请求
+type ReturnRefundRequest struct {
+	ID     uint   `json:"-" params:"id" path:"id" validate:"required" description:"退款申请ID"`
+	Remark string `json:"remark" validate:"omitempty,max=500" maxLength:"500" description:"退回备注"`
+}
+
+// RefundListRequest 退款申请列表查询请求
+type RefundListRequest struct {
+	Page     int   `json:"page" query:"page" validate:"omitempty,min=1" minimum:"1" description:"页码（默认1）"`
+	PageSize int   `json:"page_size" query:"page_size" validate:"omitempty,min=1,max=100" minimum:"1" maximum:"100" description:"每页数量（默认20，最大100）"`
+	Status   *int  `json:"status" query:"status" validate:"omitempty,min=1,max=4" minimum:"1" maximum:"4" description:"状态 (1:待审批, 2:已通过, 3:已拒绝, 4:已退回)"`
+	OrderID  *uint `json:"order_id" query:"order_id" validate:"omitempty" description:"关联订单ID"`
+	ShopID   *uint `json:"shop_id" query:"shop_id" validate:"omitempty" description:"店铺ID"`
+}
+
+// RefundResponse 退款申请详情响应
+type RefundResponse struct {
+	ID                    uint   `json:"id" description:"退款申请ID"`
+	RefundNo              string `json:"refund_no" description:"退款单号"`
+	OrderID               uint   `json:"order_id" description:"关联订单ID"`
+	PackageUsageID        *uint  `json:"package_usage_id,omitempty" description:"关联套餐使用记录ID"`
+	ShopID                *uint  `json:"shop_id,omitempty" description:"店铺ID"`
+	ActualReceivedAmount  int64  `json:"actual_received_amount" description:"实收金额（分）"`
+	RequestedRefundAmount int64  `json:"requested_refund_amount" description:"申请退款金额（分）"`
+	ApprovedRefundAmount  *int64 `json:"approved_refund_amount,omitempty" description:"审批实际退款金额（分）"`
+	RefundReason          string `json:"refund_reason" description:"退款原因"`
+	Status                int    `json:"status" description:"状态 (1:待审批, 2:已通过, 3:已拒绝, 4:已退回)"`
+	ProcessorID           *uint  `json:"processor_id,omitempty" description:"审批人ID"`
+	ProcessedAt           string `json:"processed_at,omitempty" description:"审批时间"`
+	RejectReason          string `json:"reject_reason,omitempty" description:"拒绝原因"`
+	Remark                string `json:"remark,omitempty" description:"审批备注"`
+	CommissionDeducted    bool   `json:"commission_deducted" description:"佣金是否已回扣"`
+	AssetReset            bool   `json:"asset_reset" description:"资产是否已重置"`
+	Creator               uint   `json:"creator" description:"创建人ID"`
+	Updater               uint   `json:"updater" description:"更新人ID"`
+	CreatedAt             string `json:"created_at" description:"创建时间"`
+	UpdatedAt             string `json:"updated_at" description:"更新时间"`
+}
+
+// RefundListResponse 退款申请列表分页响应
+type RefundListResponse struct {
+	Items []RefundResponse `json:"items" description:"退款申请列表"`
+	Total int64            `json:"total" description:"总记录数"`
+	Page  int              `json:"page" description:"当前页码"`
+	Size  int              `json:"size" description:"每页数量"`
+}