refactor(module-llm):优化知识库字符串处理逻辑

- 移除了不必要的空字符串赋值操作
- 添加了对 knowledgeBase

yudao-module-llm/yudao-module-llm-biz/src/main/java/cn/iocoder/yudao/module/llm/service/conversation/ConversationServiceImpl.java

@@ -434,19 +434,19 @@ public class ConversationServiceImpl implements ConversationService {
         String knowledgeBaseString="";
         if (chatReqVO.getKnowledge() != null) {
             StringBuilder knowledgeBase = getKnowledgeBase(chatReqVO);
-             knowledgeBaseString = knowledgeBase.toString();
+            knowledgeBaseString = knowledgeBase.toString();
 
-             if (org.apache.commons.lang3.StringUtils.isBlank(knowledgeBaseString)){
-                 knowledgeBaseString="";
-             }
+            // 处理 knowledgeBaseString
+            if (StringUtils.isNotBlank(knowledgeBaseString)) {
+                knowledgeBaseString = "<context>" + knowledgeBaseString + "</context>";
+            }
 
             // 处理 systemPrompt
-             systemPrompt = StringUtils.isBlank(chatReqVO.getSystemPrompt())
+            systemPrompt = StringUtils.isBlank(chatReqVO.getSystemPrompt())
                     ? PROMPT
                     : chatReqVO.getSystemPrompt() + "\n" + PROMPT;
-
         }
-        String mess = systemPrompt +  "<content>"+knowledgeBaseString+"</content>";
+        String mess = systemPrompt + knowledgeBaseString;
 
         // 查询历史记录消息，并将查询出来的知识信息放入到 role = system 的消息中
         List<String> messageHistoryList = stringRedisTemplate.opsForList().range(CHAT_HIStORY_REDIS_KEY + ":" + chatReqVO.getUuid(), 0, -1);