Back in the days when I wrote the code, I didn't know about the
`require` package yet. Using `require.NoError()` makes the test code
more straight-forward.
No functional changes, except that when tests fail, they now fail
without panicking.
Add a "Last Rendered" view to the webapp.
The Manager now stores (in the database) which job was the last
recipient of a rendered image, and serves that to the appropriate
OpenAPI endpoint.
A new SocketIO subscription + accompanying room makes it possible for
the web interface to receive all rendered images (if they survive the
queue, which discards images when it gets too full).
