fix(trading-service): correct global prefix to match Kong routing

Change prefix from 'api/v2' to 'api/v2/trading' to match Kong gateway
configuration with strip_path: false.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/trading-service/src/main.ts

@@ -20,7 +20,7 @@ async function bootstrap() {
     credentials: true,
   });
 
-  app.setGlobalPrefix('api/v2');
+  app.setGlobalPrefix('api/v2/trading');
 
   const config = new DocumentBuilder()
     .setTitle('Trading Service API')