🔐 로그인 시 비밀번호 은닉

## 📃이슈내용
로그인 시 비밀번호 은닉

## 🏷상세내용
- JWT or Crypto로 비밀번호 저장

## ❗체크리스트
- [ ] ...

## 🔎래퍼런스
- [Node.js 해시값 계산](https://comocloud.tistory.com/187)
- [JWT로 로그인 유지](https://velog.io/@taemin4u/JWT%EB%A1%9C-%EB%A1%9C%EA%B7%B8%EC%9D%B8-%EB%B0%8F-%EB%A1%9C%EA%B7%B8%EC%9D%B8-%EC%9C%A0%EC%A7%80%ED%95%98%EA%B8%B0feat.-Next-JS)

The issue mentions using JWT or Crypto for password storage, but does not specify current code location or what 'password hiding' means. Look for existing authentication logic, likely in API routes or middleware. Check if passwords are currently stored in plaintext and research secure hashing with bcrypt or similar. The provided references are in Korean and discuss JWT for login persistence and Node.js hash calculation.

Written by the indexing model from the issue text.