Add button component in the Header component

After the button component is merged and we have it, use it in the Header component and delete the styles which is related to the button in the header.

Find the Header component and the new button component in the codebase. Replace the existing button markup in the Header with the new button component, then remove any button-specific styles from the Header's CSS or styling files. Verify the changes by running the project locally to ensure the button appears and functions correctly.

索引モデルが issue の本文から書いたものです。