Big Style Update - Githubissues

This PR is on the bigger side, but I hope the changes and commits are atomic enough to make review of this easier.

The Gist

This drastically changes the front page to what I hope is something that explains what the conference is and provides more concrete call to actions that users can take.
I added in our overall conference theme and colors, instead of the default rainbow. It exists in the app.css, Colors.tsx, and the tailwind config. At some point it can probably be standardized, by my main goal for now is to just get this out the door.
I had a bit too much fun with the sidebar, but I enjoy the color scheme and the effects for hovering/clicking to a page. Same thing goes for the images on the main site.
All .mdx pages got a small style update to make the headers consistent. Additionally I added some callouts to bring attention to what is open/closed.
I did merge in the latest changes from main and de-conflicted. So it should be good to merge straight away.