[task] header (component)

### ISSUE
- Group: `client`
-Type: `feature`
-Detail: header bar(component)

### TODO
1. [ ] 로고
2. [ ] 로그인(로그아웃)
3. [ ] 회원가입(로그인 중에는 개인정보)
4. [ ] display-flex(반응형)

### Estimated time
>Pick one

### `1h`

Start in the client area and locate the existing header component or frontend entry point. Implement the listed logo, login/logout, signup and logged-in personal-information states, then verify the header uses flex layout responsively; no test or file is named in the issue.

Written by the indexing model from the issue text.