修改rag，实现混合检索

backend/app/main_graph/utils/rag_initializer.py

@@ -1,5 +1,5 @@
 # app/rag_initializer.py
-from app.rag.tools import create_rag_tool_sync
+from app.rag.tools import create_rag_tool_sync, create_rag_tool_async
 from rag_core import create_parent_retriever
 from app.model_services import get_embedding_service
 from app.logger import info, warning
@@ -16,11 +16,11 @@ async def init_rag_tool(local_llm_creator):
             embeddings=embeddings
         )
         rewrite_llm = local_llm_creator()
-        rag_tool = create_rag_tool_sync(
+        rag_tool = create_rag_tool_async(
             retriever, rewrite_llm,
             num_queries=3, rerank_top_n=5
         )
-        info("✅ RAG 检索工具初始化成功")
+        info("✅ RAG 检索工具初始化成功（异步版本）")
         return rag_tool
     except Exception as e:
         warning(f"⚠️ RAG 检索工具初始化失败: {e}")