Improve Menu graphics

[TheoPannetier]

Context

The menu we have so far is functional, but really ugly. It would be great if we could graphically improve it, so that the game is a bit more inviting to players and developers alike. Nice graphics are inspiring, after all.

The other day @richelbilderbeek and I AI-generated some cool (and eerie) dragon artwork (see the resource folder on the richel branch). Using one of those as a background could be a good step towards this.

Another increment could be to improved the menu buttons themselves, e.g. using a nicer font, and maybe some proper artwork for the frames.