NHT: Keyboard shortcuts to add stats

This still needs to be defined. Work with power users to figure out what these should be. Some starting suggestions:
- `j` and `k` or `↑` and `↓` to nav through lists
- Make a non-``-based list for stat type so it can be moved through with `j` and `k`?
- Ensure tabbing through form controls works as expected and is intuitive ([`tabindex`](https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/tabindex)?)
- Possibly add specific keybindings per-stat? Maybe not though... simply fixing tabbing through UI elements and moving up and down lists may be enough