Restore asdf/rtx config, restore dev shell script

[booniepepper]

Too useful to my workflow to leave out.

I moved the dev dt to dev/dt so folks don't call it by accident. It retains an error message for anyone lost.

I did try to do this in dt instead of bash but it's not ready yet. I'd need a way to execute a child process and stream stdin from it. Maybe something like exec-stream but I want to think on that and not be hasty