feat(system): 实现注册码功能并优化用户注册流程

- 新增注册码生成和验证功能- 实现系统设置管理，包括注册功能开关
- 更新前端界面，增加系统管理和注册码相关功能
- 修改数据库结构，添加系统设置和注册码表

biji-houdaun/src/main/java/com/test/bijihoudaun/entity/RegistrationCode.java

@@ -0,0 +1,34 @@
+package com.test.bijihoudaun.entity;
+
+import com.baomidou.mybatisplus.annotation.IdType;
+import com.baomidou.mybatisplus.annotation.TableId;
+import com.baomidou.mybatisplus.annotation.TableName;
+import io.swagger.v3.oas.annotations.media.Schema;
+import lombok.Data;
+
+import java.io.Serializable;
+import java.time.LocalDateTime;
+
+@Data
+@TableName("registration_codes")
+@Schema(description = "注册码实体")
+public class RegistrationCode implements Serializable {
+
+    private static final long serialVersionUID = 1L;
+
+    @TableId(type = IdType.AUTO)
+    @Schema(description = "主键ID", name = "id")
+    private Long id;
+
+    @Schema(description = "注册码", name = "code")
+    private String code;
+
+    @Schema(description = "过期时间", name = "expiryTime")
+    private LocalDateTime expiryTime;
+
+    @Schema(description = "创建者", name = "createdBy")
+    private String createdBy;
+
+    @Schema(description = "创建时间", name = "createdAt")
+    private LocalDateTime createdAt;
+}