Heading level skips (e.g. H2 to H4 without H3) WAI/WCAG violations

[kheiner]

https://www.w3.org/WAI/tutorials/page-structure/headings/

Skipping heading ranks can be confusing and should be avoided where possible: Make sure that a <h2> is not followed directly by an <h4>, for example. It is ok to skip ranks when closing subsections, for instance, a <h2> beginning a new section, can follow an <h4> as it closes the previous section.

Asked my 🤖 buddy Claude to sweep for them after manually finding #824

[linear-code]

EDU-537