feat: Add user existence checks to economy commands and refactor trade service to expose sessions for testing.

src/modules/trade/trade.service.ts

@@ -71,6 +71,8 @@ const processTransfer = async (tx: Transaction, from: TradeParticipant, to: Trad
 };
 
 export const tradeService = {
+    // Expose for testing
+    _sessions: sessions,
     /**
      * Creates a new trade session
      */