chore: 调整开发环境默认检索引擎

- 将 rag.engine 默认值切换为 lucene

- 补充知识检索相关配置注释

easyflow-starter/easyflow-starter-all/src/main/resources/application.yml

@@ -208,7 +208,9 @@ jetcache:
 
 # 多路召回搜索引擎配置
 rag:
-  engine: ES
+  # 搜索引擎选择，lucene/ES
+  engine: lucene
+  # 向量数据库配置
   milvus:
     uri: http://127.0.0.1:39530
     databaseName: default
@@ -216,6 +218,7 @@ rag:
     username: easyflowadmin
     password: easyflowadmin123
     autoCreateCollection: true
+  # 搜索引擎配置
   searcher:
     lucene:
       indexDirPath: /Users/slience/data/easyflow/luceneKnowledge