feat: 新增 ScriptMessageService 接口

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/src/main/java/com/emotion/service/ScriptMessageService.java

@@ -0,0 +1,25 @@
+package com.emotion.service;
+
+import com.emotion.dto.response.MessageResponse;
+import java.util.List;
+
+/**
+ * 剧本消息版本管理服务
+ */
+public interface ScriptMessageService {
+
+    /**
+     * 获取对话下的消息历史
+     */
+    List<MessageResponse> listByConversation(String conversationId, boolean includeVersions);
+
+    /**
+     * 获取某条消息的版本链
+     */
+    List<MessageResponse> getVersions(String messageId);
+
+    /**
+     * 删除指定版本消息
+     */
+    boolean deleteVersion(String messageId);
+}