[Client] 로그인 Modal창 구현

### ISSUE
***
Group
- [ ] client
- [ ] server
- [ ] sr

Type
- [ ] bug
- [ ] feature
- [ ] add
- [ ] delete

description
> 로그인 버튼을 누르면 나오는 Modal창을 구현합니다.

### TODO
***
1. [ ] job 1
2. [ ] job 2
3. [ ] job 3

### Estimated time
***
> 3h

No file or test is named. Start by locating the client-side login button and checking whether the project already has modal components or patterns. Done means a modal appears when the login button is pressed; confirm the existing client checks or manual flow if available.

Rédigé par le modèle d'indexation à partir du texte de l'issue.