refactor(database): 更新数据库配置和实体映射

- 修改数据库连接URL地址
- 为所有实体类添加@TableField注解映射数据库字段
- 使用反引号标识符包裹表名和字段名
- 更新SQL查询语句使用明确字段列表
- 在配置文件中启用MyBatis安全模式防止SQL注入
- 添加MarkdownFileVO中groupingName字段的exist = false标识

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

@@ -1,6 +1,7 @@
 package com.test.bijihoudaun.entity;
 
 import com.baomidou.mybatisplus.annotation.IdType;
+import com.baomidou.mybatisplus.annotation.TableField;
 import com.baomidou.mybatisplus.annotation.TableId;
 import com.baomidou.mybatisplus.annotation.TableName;
 import io.swagger.v3.oas.annotations.media.Schema;
@@ -9,7 +10,7 @@ import lombok.Data;
 import java.io.Serializable;
 
 @Data
-@TableName("registration_codes")
+@TableName("`registration_codes`")
 @Schema(description = "注册码实体")
 public class RegistrationCode implements Serializable {
 
@@ -17,17 +18,22 @@ public class RegistrationCode implements Serializable {
 
     @TableId(type = IdType.AUTO)
     @Schema(description = "主键ID", name = "id")
+    @TableField("id")
     private Long id;
 
     @Schema(description = "注册码", name = "code")
+    @TableField("`code`")
     private String code;
 
     @Schema(description = "过期时间", name = "expiryTime")
+    @TableField("expiry_time")
     private String expiryTime;
 
     @Schema(description = "创建者", name = "createdBy")
+    @TableField("created_by")
     private String createdBy;
 
     @Schema(description = "创建时间", name = "createdAt")
+    @TableField("created_at")
     private String createdAt;
-}
+}