Accessibility conformance for 1.9: clarity VPAT and verified fixes

[ajrbyers]

Updates the accessibility conformance data (src/a11y/conformance_data.json) and the regenerated docs/md/a11y_conformance.md for 1.9.

Merge after #5614. The clarity rows and Material 1.4.10 depend on fixes in that PR.

Clarity

A new "Front of House - Clarity Theme" area covers all 55 criteria. The ratings come from the clarity sweep of the evaluation sample after #5613 and #5614, from browser testing, and from what clarity shares with the other themes. Each row links its existing criterion issue.

Rating	Criteria
Supports	36
Partially supports	7 (1.3.1, 2.4.2, 2.4.4, 2.4.6, 2.5.3, 3.3.2, 4.1.2)
Not applicable	12, as in the other themes

2.4.2 has since moved to Supports (see below), so clarity has 37 Supports and 6 Partials.

Fixes merged in 1.9, flipped after testing each one by hand

Theme	Criterion	Change	Fixed by
OLH	1.3.3	Partial → Supports	toastr removed from reader pages (#5107)
OLH	2.2.1	Partial → Supports	Log-out message no longer times out (#5196)
OLH	2.4.3	Partial → Supports	Figure lightbox close button focusable (#5277)
OLH, Material, Clean	2.4.7	Partial → Supports	Carousel focus visible (#5278)
OLH, Material, Clean	3.2.2	Partial → Supports	Language no longer changes on input (#5280)
OLH, Clean	3.1.1	Partial → Supports	Print pages declare their language (#5176)
OLH, Material, Clean	4.1.3	N/A → Supports	Messages announced (#5107, #5613)
Material, Clean	2.1.1	Partial → Supports	Scrollable areas focusable (#5589)
Material	1.4.10	Partial → Supports	News list reflows at 320px (#5614)
Material	2.2.1	stays Partial	Remark is now "Carousel cannot be paused."
Clean	1.3.4	Partial → Supports	Portrait carousel with long titles (#5142)
Clean	2.5.8	Partial → Supports	Target sizes (#5276)

2.4.2 Page Titled: Supports in every theme. It uses the same values as draft #5564 (#5563, 3b23ea89d), so the two PRs agree.

Summary

The description at the top now says we test with both manual and automated methods, using a range of tools.

[StephDriver]

To keep this consistent with the existing audit work:

1. all changes which still linked to their previous audit issue now link here as the latest update.
2. all changes that had been linked to work done issue rather than an audit issue have also been linked here as the place where they were audited after that work was done. The column is for audits, not for bugfixes.
3. updated the remarks so they make sense when a single theme is visible (as on the accessibility page of a journal) rather than 'see other themes'.
4. where this work did not change an audit result or remark (as with some of the N/A in clarity) I restored the original line which already had a more detailed explanation for that result.