Update app.py

app.py

@@ -11,6 +11,7 @@ from langchain_community.tools import DuckDuckGoSearchRun
 from langchain_huggingface import HuggingFaceEndpoint
 from langgraph.graph import StateGraph, END
 from langgraph.prebuilt import ToolNode
+from langchain import hub
 
 # --- Main Application Logic ---