Fix router: rag fallback to direct_answer instead of logic_solver

src/nodes/router.py

@@ -109,5 +109,6 @@ def route_question(state: GraphState) -> Literal["knowledge_rag", "logic_solver"
         return "direct_answer"
     if route == "math":
         return "logic_solver"
-    # Fallback to logic_solver instead of RAG (no vector DB in production)
-    return "logic_solver"
+    # Fallback to direct_answer for RAG questions (no vector DB in production)
+    # Direct agent can answer general knowledge questions using LLM knowledge
+    return "direct_answer"