fixed typo

app.py

@@ -16,7 +16,7 @@ class BasicAgent:
     """A langgraph agent."""
     def __init__(self):
         print("BasicAgent initialized.")
-        self.graph = build_graph()
+        self.graph = graph()
 
     def __call__(self, question: str) -> str:
         print(f"Agent received question (first 50 chars): {question[:50]}...")