fix issues in core

core/racing/domain/value-objects/Money.ts

@@ -3,11 +3,14 @@
  * Represents a monetary amount with currency and platform fee calculation
  */
  
-import { RacingDomainValidationError } from '../errors/RacingDomainError';
 import type { IValueObject } from '@core/shared/domain';
+import { RacingDomainValidationError } from '../errors/RacingDomainError';
 
 export type Currency = 'USD' | 'EUR' | 'GBP';
 
+export const isCurrency = (value: string): value is Currency =>
+  value === 'USD' || value === 'EUR' || value === 'GBP';
+
 export interface MoneyProps {
   amount: number;
   currency: Currency;
@@ -34,6 +37,7 @@ export class Money implements IValueObject<MoneyProps> {
     return new Money(amount, currency);
   }
 
+  // TODO i dont think platform fee must be coupled 
   /**
    * Calculate platform fee (10%)
    */