[Task] 회원가입, 로그인 api 구현

### ISSUE
- Group: `server`
- Type: `feature`
- Detail: - 회원가입, 로그인 api 구현

### TODO
1. [x] 회원가입 controller 작성
2. [x] 로그인 controller 작성
3. [x] postman을 통한 테스트 진행

### Estimated time
### `3h`

The issue identifies the server group and says to implement signup and login APIs. Review the existing signup and login controllers first, then inspect the Postman tests mentioned in the completed checklist. Done would require a clearly defined remaining change and passing API tests, but the payload does not identify an unfinished task.

Written by the indexing model from the issue text.