feat(oa): 添加 AI 对话管理功能

- 新增 AI配置、对话历史、对话消息等相关的实体类、Mapper、Service 和 Controller
- 实现 AI 对话管理的基础功能，包括创建对话、发送消息、结束对话等- 集成 DeepSeek AI 服务，实现与 AI 模型的交互
- 添加 token消耗和费用计算相关逻辑

ruoyi-oa/src/main/resources/mapper/oa/SysOaAiMessageMapper.xml

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<!DOCTYPE mapper
+PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
+"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
+<mapper namespace="com.ruoyi.oa.mapper.SysOaAiMessageMapper">
+
+    <resultMap type="SysOaAiMessageVo" id="SysOaAiMessageResult">
+        <result property="messageId" column="message_id"/>
+        <result property="conversationId" column="conversation_id"/>
+        <result property="role" column="role"/>
+        <result property="content" column="content"/>
+        <result property="tokens" column="tokens"/>
+        <result property="cost" column="cost"/>
+        <result property="messageOrder" column="message_order"/>
+        <result property="createTime" column="create_time"/>
+        <result property="createBy" column="create_by"/>
+    </resultMap>
+
+    <sql id="selectSysOaAiMessageVo">
+        select message_id, conversation_id, role, content, tokens, cost, message_order, create_time, create_by
+        from sys_oa_ai_message
+    </sql>
+
+    <select id="selectMessagesByConversationId" parameterType="Long" resultMap="SysOaAiMessageResult">
+        <include refid="selectSysOaAiMessageVo"/>
+        where conversation_id = #{conversationId}
+        order by message_order asc
+    </select>
+
+</mapper>