feat: 初始化后端项目基础架构

添加项目基础配置文件和目录结构
实现用户、角色、权限等核心模块的实体类、Mapper接口和服务层
配置数据库连接和MyBatis-Plus支持
添加统一响应格式和异常处理机制

src/main/java/com/qf/backend/entity/Refunds.java

@@ -0,0 +1,36 @@
+package com.qf.backend.entity;
+
+import com.baomidou.mybatisplus.annotation.IdType;
+import com.baomidou.mybatisplus.annotation.TableId;
+import com.baomidou.mybatisplus.annotation.TableName;
+import lombok.Data;
+import java.math.BigDecimal;
+import java.util.Date;
+
+/**
+ * 退款信息表
+ */
+@Data
+@TableName("refunds")
+public class Refunds {
+    
+    @TableId(type = IdType.AUTO)
+    private Long id;
+    
+    private String refundNo;
+    private Long orderId;
+    private Long orderItemId;
+    private Long userId;
+    private Long shopId;
+    private BigDecimal refundAmount;
+    private String refundReason;
+    private String refundType; // 退款类型
+    private Integer refundStatus; // 0: 申请中, 1: 退款成功, 2: 退款失败, 3: 已拒绝
+    private String refundAccount;
+    private String transactionId;
+    private Date applyTime;
+    private Date processTime;
+    private String processRemark;
+    private Date createdAt;
+    private Date updatedAt;
+}