Rather than building up the HTML manually with JavaScript, since our layout is quite simple, let's just move this to a HTML file that the script can load and hydrate. I think the result will be more maintainable.

We don't have access to a templating library, but since we only have a couple of variables to inject we can just do this manually. There can still be some dynamic JavaScript as necessary but we don't need to build the entire template that way.

This also makes it easier to use a CSS block in rather than inlining all the styles for each block. We could also consider putting that in its own dedicated file and have the script load and inject it, although the style is pretty simple that it may not be worth it.

It would be nice if you could just open the html file locally (file://) to iterate on the design, and this code would just make it work within the VS Code webview context.