Fix version mismatch

Author: piyushroshan

services/chatbot/requirements.txt

@@ -6,6 +6,7 @@ langchain-openai==1.0.1
 langchain-text-splitters==1.0.0
 langchain-mcp-adapters==0.1.11
 langgraph==1.0.2
+langgraph-prebuilt<1.0.9
 chromadb==1.3.0
 langchain-chroma==1.0.0
 openai==2.6.1