Setup API tests

[casperiv0]

To keep SnailyCAD maintainable, we need tests. We have a lot of API routes which are not tested, only tested during development. This is fine, but comes with a large drawback: when a new feature is added, parts of the code get changed, therefore sometimes stuff could break.
Tests can assure us that the feature will break or continue working on feature additions or large changes.

This is a rather extremely large task, but should pay off in the longer run. We should do this incrementally to make sure we test everything properly.

Additional Context

• https://vitest.dev/
• https://tsed.io/docs/testing.html#unit-test
• https://tsed.io/tutorials/session.html#usage
• https://stackoverflow.com/questions/70674664/how-to-build-run-and-call-docker-container-in-github-action
• PostgreSQL database in GitHub CI