a11y: narrow-viewport sidebar toolbar is a nav landmark with no links #14868

The bar that appears below the navbar under the lg breakpoint is marked up as a
nav, so it becomes a navigation landmark. It holds the sidebar toggle button,
the page title or the breadcrumbs, and the search button. In neither
configuration does the nav itself hold a navigation link.

• With breadcrumbs on (the default), every link is inside a nested
  nav.quarto-page-breadcrumbs, which is its own landmark. The postprocessor
  swaps it in for the title element:
  

  quarto-cli/src/project/types/website/website-navigation.ts

  Lines 470 to 482 in 093316c

  	const secondaryNavTitleEl = doc.querySelector(
  	".quarto-secondary-nav .quarto-secondary-nav-title",
  	);
  	if (secondaryNavTitleEl) {
  	if (showBreadCrumbs) {
  	const navEl = makeBreadCrumbs(doc);
  	if (secondaryNavTitleEl.parentElement) {
  	secondaryNavTitleEl.parentElement.replaceChild(
  	navEl,
  	secondaryNavTitleEl,
  	);
  	}
  	} else {

• With breadcrumbs: false there are no links at all. The <a> at L74 and L78
  has no href. It is a Bootstrap collapse trigger, and Make website sidebar section toggles keyboard-operable buttons #14826 already removed
  the role="navigation" and role="link" it used to carry.

So the landmark holds a button, a heading, and another landmark.

The strip only exists below lg, and the sidebar it toggles is a collapse that
sits under it, so both are in the accessibility tree together when a reader opens
the sidebar:

This surfaced in review of #14813, which gives every nav landmark a distinct
aria-label. Naming this one is hard because there is no honest navigation word
for it. The label there is Toolbar, which a screen reader announces as
"Toolbar, navigation".

axe does not flag this. landmark-unique only requires that the labels differ,
which #14813 satisfies. This is a markup question, not a rule violation.

Suggested fix

Change the nav to a div and drop its aria-label. The nested breadcrumbs
nav keeps its own landmark and label, so the only difference for a reader is
that the Toolbar entry drops out of the landmark list. Nothing else moves, and
no links become unreachable.

Points to check:

• Most CSS selectors are class based (.quarto-secondary-nav), but four rules
  use the element selector nav.quarto-secondary-nav and need updating.
• With breadcrumbs: false the bar then holds no landmark at all. Make sure the
  page title inside it is still reachable.
• The navigation-toolbar-label language key added by Give every website and book nav landmark a distinct, localizable label #14813 becomes unused. It
  ships in _language.yml and in all 33 translated files, so remove it before
  1.11 is released rather than after.

Split from #14813. Part of #8706.

Investigated with AI (Claude Code), grounded in a local clone.