[Client] Main page 배너 생성

### ISSUE
- Type: `main page`
- Detail: main page architecture

### TODO
1. [ ] 배너 생성
2. [ ] 백그라운드 이미지 추가
3. [ ] 퀴즈 시작하기, 로그인 버튼 추가
4. [ ] 배너 문구 추가

### Estimated time
> Pick one
### `1d`

Start by locating the main page entry point and reviewing the existing client structure and available image assets. Confirm the intended banner layout and copy, then consider the work complete when the banner has a background image, banner text, and working quiz-start and login buttons on the main page.

Written by the indexing model from the issue text.