Adjust max_tokens to 450 as requested by the user

backend/main.py

@@ -123,7 +123,7 @@ def run_flow_b(message: str, api_key: str, history: Optional[List[ChatMessage]]
         model="gemini-3.1-flash-lite",
         google_api_key=api_key,
         temperature=0.5,
-        max_tokens=700,
+        max_tokens=450,
         generation_config={"response_mime_type": "application/json"}
     )