feat: 下沉知识库检索编排能力

- 新增 rag retrieval 核心协议、RRF 融合与相关度归一化

- 支持关键词检索按 knowledgeId 过滤并补充 ES/Lucene 单测

- 扩展 KnowledgeNode 检索模式与 Milvus 检索参数透传

easy-agents-search-engine/easy-agents-search-engine-service/src/main/java/com/easyagents/search/engine/service/DocumentSearcher.java

@@ -28,8 +28,12 @@ public interface DocumentSearcher {
     boolean updateDocument(Document document);
 
     default List<Document> searchDocuments(String keyword) {
-        return searchDocuments(keyword, 10);
+        return searchDocuments(KeywordSearchRequest.of(keyword, 10));
     }
 
-    List<Document> searchDocuments(String keyword, int count);
+    default List<Document> searchDocuments(String keyword, int count) {
+        return searchDocuments(KeywordSearchRequest.of(keyword, count));
+    }
+
+    List<Document> searchDocuments(KeywordSearchRequest request);
 }

easy-agents-search-engine/easy-agents-search-engine-service/src/main/java/com/easyagents/search/engine/service/KeywordSearchMetadataKeys.java

@@ -0,0 +1,9 @@
+package com.easyagents.search.engine.service;
+
+public final class KeywordSearchMetadataKeys {
+
+    private KeywordSearchMetadataKeys() {
+    }
+
+    public static final String KNOWLEDGE_ID = "knowledgeId";
+}

easy-agents-search-engine/easy-agents-search-engine-service/src/main/java/com/easyagents/search/engine/service/KeywordSearchRequest.java

@@ -0,0 +1,39 @@
+package com.easyagents.search.engine.service;
+
+public class KeywordSearchRequest {
+
+    private String keyword;
+    private int count = 10;
+    private String knowledgeId;
+
+    public static KeywordSearchRequest of(String keyword, int count) {
+        KeywordSearchRequest request = new KeywordSearchRequest();
+        request.setKeyword(keyword);
+        request.setCount(count);
+        return request;
+    }
+
+    public String getKeyword() {
+        return keyword;
+    }
+
+    public void setKeyword(String keyword) {
+        this.keyword = keyword;
+    }
+
+    public int getCount() {
+        return count;
+    }
+
+    public void setCount(int count) {
+        this.count = count <= 0 ? 10 : count;
+    }
+
+    public String getKnowledgeId() {
+        return knowledgeId;
+    }
+
+    public void setKnowledgeId(String knowledgeId) {
+        this.knowledgeId = knowledgeId;
+    }
+}