catch InvalidPuzzleCodeExceptions for nicer command-line UI?

[dandrake]

In CommandLine.java, I added a catch for InvalidPuzzleCodeException`, in addition to the generic exception catching -- it's not clear if that's the best thing here. Do we want a super-polished UI? Or keep it simple, since after all the students in this class are learning about how to deal with errors and crashes and sometimes-mysterious messages.

The question here is 100% about the usability of what people see on the CLI.

Let's pull this into a separate PR so it doesn't hold up “puzzle show.” We could also consider suppressing the unhelpful Gradle output as part of that PR.

Originally posted by @pcantrell in #18 (comment)

[dandrake]

There's a little more discussion in a different issue that I made on the course site repo, which is not at all where it belongs, but worth checking out: https://codeberg.org/pcantrell/comp127-ssg/issues/21