Integrate commitlint.

[Ross-Esmond]

Bring in Commitlint for both local pre-checks and a GitHub actions failure. They have a config for Angular-style commit messages that will catch the most common issues.

Considered alternatives
None. Commitlint appears to be the most popular commit message checker on npm by a wide margin.

Additional context
This will help to avoid having to "confront" people about their commit messages if they miss the guide.

[Ross-Esmond]

I think #3 should also happen. I have definitely forgotten to rerun some of the commands before pushing a few times now. A local error saves a lot of time, even when you know what you're doing. Catching a bad commit message before the commit saves a ton of time in particular.

[aarthificial]

Done in 6c8d190