feat(minion): switch to zsh #10

I've installed zsh, including
- zsh4humans
- powerlevel10k

This is because
- I'm interested installing atuin, and we've had some problems using it
with bash
- I'm interested in adding jujutsu information to my prompt, and zsh
will let me do this much more easily than bash

This isn't an ingredient of its own yet because it doesn't integrate
nicely with, say, catppuccin (or really anything that isn't itself) but
it's a start...