Run an automated code review on gonext's own pull requests

Part of #44. Came out of an ideation session, not a scoped request.

Wire the chosen code review tool into this repository's pull request flow so every PR gets a machine pass in addition to human review.

Worth noting up front: this repository has no CI at all today — there is no `.github/workflows/` directory, and the only workflow in the tree is `templates/.github/workflows/ci.yml`, which ships to generated projects rather than running here. So this issue either depends on standing up CI for gonext first, or has to bring it along.

Start with issue #44 and inspect the repository root for the absent .github/workflows/ directory. Compare templates/.github/workflows/ci.yml carefully, since it serves generated projects rather than gonext itself. Done means every pull request to gonext receives an automated code-review pass alongside human review.

Written by the indexing model from the issue text.