fix tests, add CI, fix on mac, extend docs (#25)

* tests: fix float problems and PAT problem

* extend CONTRIBUTING.md

* extend build documentation, add GH action, fix build on MacOS

* fix build on Vercel

* update .gitignore and CONTRIBUTING.md

* fix all tests

* add backend tests to CI

* make e2e tests work

* add debug log to e2e test

* ignore copied tests in CI

docs/deploy.md

@@ -62,6 +62,9 @@ Click on the deploy button to get started!
     ![](https://files.catbox.moe/0yclio.png)
 11. As `Root directory` select the `backend` folder.
 12. Click deploy, and you're good to go. See your domains to use the API!
+13. optional: add an SQL database; by using e.g. the ["Nile" integration](https://vercel.com/marketplace/nile) or by manually setting the environment variable `POSTGRES_URL`
+14. optional: [create your own OAuth App](https://github.com/settings/developers) and set environment variables `OAUTH_REDIRECT_URI`, `OAUTH_CLIENT_ID` and `OAUTH_CLIENT_SECRET` on Vercel accordingly
+15. optional: in addition to the Vercel project based on the `backend` folder, create a second project based on the `frontend/frontend` folder. No environment variables needed.
 
 </details>