refactor: update default similarityThreshold (spring-ai-alibaba#281)

---------

Co-authored-by: lzq986 <2719916844@qq.com>

Author: VLSMB

data-agent-management/src/main/java/com/alibaba/cloud/ai/dataagent/config/DataAgentProperties.java

@@ -139,7 +139,7 @@ public static class VectorStoreProperties {
 		/**
 		 * 相似度阈值配置，用于过滤相似度分数大于等于此阈值的文档
 		 */
-		private double similarityThreshold = 0.2;
+		private double similarityThreshold = 0.4;
 
 		/**
 		 * 一次删除操作中，最多删除的文档数量

data-agent-management/src/main/java/com/alibaba/cloud/ai/dataagent/dto/search/AgentSearchRequest.java

@@ -31,7 +31,7 @@ public class AgentSearchRequest implements java.io.Serializable {
 	private String docVectorType;
 
 	@Builder.Default
-	private Double similarityThreshold = 0.2;
+	private Double similarityThreshold = 0.4;
 
 	private String query;