There are still there. I changed the repo name a while back to SDK so perhaps the link you are using is no longer redirecting. The correct location is https://github.com/extnd/SDK
Oh, and the files are under the ODP/WebContent folder. That's another change that was done and maybe that's why you don't see the js/css files.
ODP is the on-disk-project of the actual database so that developers can re-create the nsf with the agents and other 'domino' specific resources. I'm trying to make it so that developers don't have to wait for a new nsf but instead just create their own from the ODP and keep their on nsf in-sync with the contents from github.