Improve automated accessibility test report

Some ideas for further improving the automated accessibility test report. Can be split.

- [ ] format a nice report file as HTML with links or something that works well in CI artifact as report
- [x] link screenshots to the report
- [ ] add more accessibility testing hooks to the other tests
- commit accessibility test report to GitHub like the permissions docs? It is a little bit difficult to navigate to the report artifact right now
- [ ] separate checker to the build for accessibility that fails for new defects

Start by reviewing the existing automated accessibility test report and how its screenshots are exposed in CI artifacts. Choose one unchecked proposal, define its scope, and consider the report, additional test hooks, or build checker complete only when the intended CI behavior is reproducible and documented.

Written by the indexing model from the issue text.