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/handler/admin/refund.go

@@ -0,0 +1,150 @@
+package admin
+
+import (
+	"strconv"
+
+	"github.com/gofiber/fiber/v2"
+
+	"github.com/break/junhong_cmp_fiber/internal/model/dto"
+	refundService "github.com/break/junhong_cmp_fiber/internal/service/refund"
+	"github.com/break/junhong_cmp_fiber/pkg/errors"
+	"github.com/break/junhong_cmp_fiber/pkg/response"
+)
+
+// RefundHandler 退款管理处理器
+type RefundHandler struct {
+	service *refundService.Service
+}
+
+// NewRefundHandler 创建退款管理处理器
+func NewRefundHandler(service *refundService.Service) *RefundHandler {
+	return &RefundHandler{service: service}
+}
+
+// Create 创建退款申请
+// POST /api/admin/refunds
+func (h *RefundHandler) Create(c *fiber.Ctx) error {
+	var req dto.CreateRefundRequest
+	if err := c.BodyParser(&req); err != nil {
+		return errors.New(errors.CodeInvalidParam)
+	}
+
+	result, err := h.service.Create(c.UserContext(), &req)
+	if err != nil {
+		return err
+	}
+
+	return response.Success(c, result)
+}
+
+// List 退款申请列表
+// GET /api/admin/refunds
+func (h *RefundHandler) List(c *fiber.Ctx) error {
+	var req dto.RefundListRequest
+	if err := c.QueryParser(&req); err != nil {
+		return errors.New(errors.CodeInvalidParam)
+	}
+
+	result, err := h.service.List(c.UserContext(), &req)
+	if err != nil {
+		return err
+	}
+
+	return response.SuccessWithPagination(c, result.Items, result.Total, result.Page, result.Size)
+}
+
+// GetByID 退款申请详情
+// GET /api/admin/refunds/:id
+func (h *RefundHandler) GetByID(c *fiber.Ctx) error {
+	id, err := strconv.ParseUint(c.Params("id"), 10, 64)
+	if err != nil {
+		return errors.New(errors.CodeInvalidParam, "无效的退款申请ID")
+	}
+
+	result, err := h.service.GetByID(c.UserContext(), uint(id))
+	if err != nil {
+		return err
+	}
+
+	return response.Success(c, result)
+}
+
+// Approve 审批通过退款申请
+// POST /api/admin/refunds/:id/approve
+func (h *RefundHandler) Approve(c *fiber.Ctx) error {
+	id, err := strconv.ParseUint(c.Params("id"), 10, 64)
+	if err != nil {
+		return errors.New(errors.CodeInvalidParam, "无效的退款申请ID")
+	}
+
+	var req dto.ApproveRefundRequest
+	if err := c.BodyParser(&req); err != nil {
+		return errors.New(errors.CodeInvalidParam)
+	}
+
+	if err := h.service.Approve(c.UserContext(), uint(id), &req); err != nil {
+		return err
+	}
+
+	return response.Success(c, nil)
+}
+
+// Reject 审批拒绝退款申请
+// POST /api/admin/refunds/:id/reject
+func (h *RefundHandler) Reject(c *fiber.Ctx) error {
+	id, err := strconv.ParseUint(c.Params("id"), 10, 64)
+	if err != nil {
+		return errors.New(errors.CodeInvalidParam, "无效的退款申请ID")
+	}
+
+	var req dto.RejectRefundRequest
+	if err := c.BodyParser(&req); err != nil {
+		return errors.New(errors.CodeInvalidParam)
+	}
+
+	if err := h.service.Reject(c.UserContext(), uint(id), &req); err != nil {
+		return err
+	}
+
+	return response.Success(c, nil)
+}
+
+// Return 退回退款申请
+// POST /api/admin/refunds/:id/return
+func (h *RefundHandler) Return(c *fiber.Ctx) error {
+	id, err := strconv.ParseUint(c.Params("id"), 10, 64)
+	if err != nil {
+		return errors.New(errors.CodeInvalidParam, "无效的退款申请ID")
+	}
+
+	var req dto.ReturnRefundRequest
+	if err := c.BodyParser(&req); err != nil {
+		return errors.New(errors.CodeInvalidParam)
+	}
+
+	if err := h.service.Return(c.UserContext(), uint(id), &req); err != nil {
+		return err
+	}
+
+	return response.Success(c, nil)
+}
+
+// Resubmit 重新提交退款申请
+// POST /api/admin/refunds/:id/resubmit
+func (h *RefundHandler) Resubmit(c *fiber.Ctx) error {
+	id, err := strconv.ParseUint(c.Params("id"), 10, 64)
+	if err != nil {
+		return errors.New(errors.CodeInvalidParam, "无效的退款申请ID")
+	}
+
+	var req dto.ResubmitRefundRequest
+	if err := c.BodyParser(&req); err != nil {
+		return errors.New(errors.CodeInvalidParam)
+	}
+
+	if err := h.service.Resubmit(c.UserContext(), uint(id), &req); err != nil {
+		return err
+	}
+
+	return response.Success(c, nil)
+}