Add UI navigation plain language rule to markdown accessibility instructions

[v-rperez030]

Adds guidance on writing UI navigation steps in sequential plain language rather than relying on icon names or visual breadcrumb notation.

Two new bullets added to the Plain Language section of instructions/markdown-accessibility.instructions.md:

• Write actions as sequential steps in plain language first, using generic, stable labels rather than icon names or visual descriptions.
• A parenthetical visual reference may follow as supplemental context, but never as the sole way to describe a navigation path.

This mirrors the rule recently merged in github/accessibility-governance#3229.

[Copilot]

Pull request overview

Updates the Markdown accessibility review instructions to encourage plain-language, step-by-step UI navigation guidance that doesn’t rely on icons or visual breadcrumb notation, improving clarity for non-visual and cognitively diverse users.

Changes:

• Add a rule to describe UI navigation as sequential plain-language steps using stable labels.
• Add a rule allowing visual/icon references only as supplemental parentheticals (not the primary navigation description).

[aaronpowell]

It looks like you've incorrectly branched from the main branch not staged, and as a result all the materialised plugins are included in this PR.

You can attempt to fix this with a rebase:

git fetch origin staged
git rebase --onto origin/staged origin/main <branch name>
git push --force-with-lease

If that does not resolve it, you can run npm run plugin:clean which will delete the materialised plugins and you can commit that change.