feat: support feed role focus behaviour

[jlp-craigmorten]

When an assistive technology reading cursor moves from one article to another, assistive technologies SHOULD set user agent focus on the article that contains the reading cursor. If the reading cursor lands on a focusable element inside the article, the assistive technology MAY set focus on that element in lieu of setting focus on the containing article.

REF: https://w3c.github.io/aria/#feed