Frontend was still passing the project's URL to the backend even though
the backend had been refactored to use the project's ID. This is fixed.
Deleting the repo's files should also work now, but I do think I want to
support tracking multiple instances of the same project. This means
we'll need to check for other instances relying on the repo before
deleting it.
We need end-to-end tests 😩😩😩