Create unit tests and Github actions pipeline to improve quality control / eliminate extensive manual testing

As features continue to grow, the manual testing seems to become more and more complex.

No files, existing tests, or workflow entry points are named. Start by inspecting the repository for its current manual-testing procedures and any test or GitHub Actions configuration, then determine which behavior must be covered and how the pipeline should run. Done means the agreed manual checks are represented by unit tests and the GitHub Actions pipeline executes them successfully.

Written by the indexing model from the issue text.