fix: 移除FastJson 1.2.83严重安全漏洞，替换为Jackson

- 移除FastJson 1.2.83依赖（存在严重RCE漏洞CVE-2022-25845等）
- 替换为Spring Boot内置的Jackson 2.18.2
- 修改6个Java文件的JSON处理逻辑
- 所有模块编译验证通过

修改文件：
1. pom.xml - 移除fastjson依赖定义
2. ruoyi-common-chat/pom.xml - 替换为jackson-databind
3. QwenFileUploadUtils.java - 千问文件上传JSON解析
4. ChatRequest.java - 移除FastJson注解
5. MailSendNode.java - 邮件节点JSON处理
6. SwitcherNode.java - 条件分支JSON处理
7. AbstractAuthWeChatEnterpriseRequest.java - 企业微信登录
8. AuthDingTalkV2Request.java - 钉钉登录

安全提升：消除FastJson反序列化RCE漏洞攻击面

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ruoyi-common/ruoyi-common-chat/pom.xml

@@ -37,9 +37,10 @@
             <artifactId>ruoyi-common-sse</artifactId>
         </dependency>
 
+        <!-- FastJson已移除，使用Spring Boot自带的Jackson -->
         <dependency>
-            <groupId>com.alibaba</groupId>
-            <artifactId>fastjson</artifactId>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
         </dependency>
 
         <dependency>

ruoyi-common/ruoyi-common-chat/src/main/java/org/ruoyi/common/chat/domain/dto/request/ChatRequest.java

@@ -1,6 +1,5 @@
 package org.ruoyi.common.chat.domain.dto.request;
 
-import com.alibaba.fastjson.annotation.JSONField;
 import com.fasterxml.jackson.databind.annotation.JsonSerialize;
 import com.fasterxml.jackson.databind.ser.std.ToStringSerializer;
 import dev.langchain4j.data.message.ChatMessage;
@@ -31,7 +30,6 @@ public class ChatRequest {
      * 智能体ID。传入时后端按智能体配置解析模型/工具/技能/知识库/提示词/是否深度思考。
      */
     @JsonSerialize(using = ToStringSerializer.class)
-    @JSONField(serializeUsing = String.class)
     private Long agentId;
 
     /**
@@ -54,7 +52,6 @@ public class ChatRequest {
      * 会话id
      */
     @JsonSerialize(using = ToStringSerializer.class)
-    @JSONField(serializeUsing = String.class)
     private Long sessionId;
 
     /**
@@ -71,7 +68,6 @@ public class ChatRequest {
      * 对话id(每个聊天窗口都不一样)
      */
     @JsonSerialize(using = ToStringSerializer.class)
-    @JSONField(serializeUsing = String.class)
     private Long uuid;
 
     /**