Investigate what tools could be used to automatically check for accessibility issues

Accessibility on the web is, to put it trivially, both incredibly important and also an area that developers (at least this one) know very little about. Specifically, knowing what designs negatively affect accessibility feels really easy to forget about.

Surely there must be a well respected automated tool which we can enable in CI to warn about potential issues. We should find whatever we can easily enable and have it run as part of the UI tests.

I (Julian) am very much not a frontend expert, but I know the [ARIA guidelines](https://www.w3.org/WAI/ARIA/apg/) are one *text* reference that's relevant. Perhaps there are tools which enforce some of its recommendations.

At very least some simple checks like "ensure elements always have alt text" seem like they must exist.

Start by reviewing the repository's existing UI tests and CI configuration, then compare accessible web-testing tools against the ARIA and alt-text concerns described here. Done means selecting a practical tool and enabling it as part of the UI tests so accessibility warnings are reported in CI.

Written by the indexing model from the issue text.