Cron job to test the JS served by the production CDN

[lgarron]

• e.g. make sure https://cdn.cubing.net/js/cubing/twisty correctly populates players on a page.

We can automate this using Actions, perhaps also notify maintainers by e.g. email on failure.

[lgarron]

The healthcheck cron was added in 726e641 but it would still be a good idea to use Puppeteer/Playwright to make sure that a player full loads end-to-end.