Q6. 카드 브랜드 식별 로직 — 폼 값일까, 도메인 모델일까?

// src/components/AddCardPage/AddCardForm/index.tsx
  const [cardBrand, setCardBrand] = useState<CardBrand>({ name: '', color: '' });
  const [cardNumber, setCardNumber] = useState<CardNumberState>(['', '', '', '']);
  const [expDate, setExpDate] = useState<ExpDate>({ year: '', month: '' });
  const [password, setPassword] = useState<PasswordState>(['', '']);
  const [ownerName, setOwnerName] = useState<string>('');
  const [nickname, setNickname] = useState<string>('');
  const [CVC, setCVC] = useState<string>('');
  const [isCardBrandModalVisible, setIsCardBrandModalVisible] = useState<boolean>(false);
  const [isNicknameModalVisible, setIsNicknameModalVisible] = useState<boolean>(false);
 
  const onSelectCardBrand = (cardBrand: CardBrand) => {
    setCardBrand(cardBrand);
    setIsCardBrandModalVisible(false);
  };
 
  const onSetCardBrand = () => {
    if (cardNumber[0].length !== CARD_NUMBER_DIGITS || cardNumber[1].length !== CARD_NUMBER_DIGITS) {
      setCardBrand({ name: '', color: '' });
      return;
    }
 
    const cardBrand = CARD_BRAND[Number(cardNumber[1][3])];
 
    if (!cardBrand) {