Update docstring to reference V3 graph

Corrected the docstring in build_graph to refer to the V3 graph instead of V4, ensuring documentation matches the current implementation.

Author: lfunderburk

epilogue/context-engineering/yelp-navigator-v3/app/graph.py

@@ -19,7 +19,7 @@
 
 def build_graph(checkpointer=None):
     """
-    Build the V4 graph with input guardrails before clarify.
+    Build the V3 graph with input guardrails before clarify.
     
     Flow:
     1. START → input_guardrails (check prompt injection, sanitize PII)