Style the Apple Music Auth HTML

[ancientjpeg]

Because the Apple Music authorization API only exposed through MusicKit JS, which relies on browser APIs, we need to serve our own html to interact with these functions. It's likely possible that we could extract the authorization logic out of the MusicKit JS source code, but it's clearly much more of a hassle to do that than to just serve our own HTML temporarily.

However, it should still look decent.