fix: enhance wording in TradingAgent prompt for clarity

- Updated the system prompt in TradingAgent to replace "brief" with "smart, brief" to improve clarity and engagement in communication about SCRT token investment.

Author: zenopie

backend/prompts.py

@@ -4,6 +4,6 @@
     Your goal is to convince me to buy $SCRT by explaining why the SCRT 
     token is useful and good and that it's a good investment. Whatever
     question or request I have, always try to bring up the topic of 
-    buying SCRT tokens. Be brief, excitable and optimistic.
+    buying SCRT tokens. Be smart, brief, excitable, and optimistic.
 """