Fixes sidebar navigation not exposed as a separate navigation landmark

[jacobo-dominguez-wgu]

Description

Fixes an accessibility issue on the courseware page where the course-outline sidebar was not exposed as its own landmark and the <main> landmark included both the sidebar navigation and the primary sequence content, making the page structure unclear for screen-reader users.

After this change:

• The course-outline sidebar is a <nav> landmark with an accessible name (aria-label="Course outline").
• The <main> landmark contains only the primary sequence content; the sidebar is a sibling outside of <main>.
• The "Skip to main content" anchor (#main-content) now lives on the semantic <main> element, which is the correct WCAG-aligned skip target.

Problem

Before:

<main>                              ← includes everything
  breadcrumbs, tab nav, alerts
  <section class="outline-sidebar"> ← generic region, no accessible name
    …course outline links…
  </section>
  <div class="sequence">            ← primary content
    …unit + navigation…
  </div>
</main>

Screen readers announced a single main landmark containing both the navigation and the reading content, and the sidebar had no distinct landmark or accessible name.

Solution

After:

<div>                                                        (LoadedTabPage)
  breadcrumbs, tab nav, alerts
  <div class="container-xl d-flex flex-column flex-grow-1">
    <div class="sequence-container …">
      <nav class="outline-sidebar" aria-label="Course outline">   ← navigation landmark
        …course outline links…
      </nav>
      <main id="main-content" class="sequence w-100">             ← main landmark, primary content only
        …unit + navigation…
      </main>
      <RightSidebarSlot />
    </div>
  </div>
</div>

Non-courseware tabs (outline, dates, progress, discussion, lti_live) still receive a <main> from LoadedTabPage exactly as before — the swap is scoped to activeTabSlug === 'courseware'.

Accessibility impact

• Landmarks pass in axe / WAVE / VoiceOver rotor: the page now exposes a distinct Course outline navigation landmark and a main landmark that contains only the primary content.
• Skip link (#main-content) now targets the semantic <main> element, matching the WAI-ARIA recommendation.
• Non-courseware tabs are unchanged — their existing <main id="main-content"> landmark still wraps the tab content.

Testing

• Manual QA suggestions:
  • VoiceOver / NVDA landmark rotor on /course/:courseId/:sequenceId/:unitId should now list a navigation landmark named "Course outline" and a main landmark that does not contain the sidebar.
  • Confirm the "Skip to main content" link (if enabled by the shell/header) lands directly at the sequence content.
  • Sanity-check layout of course outline, dates, progress, discussion, and live tabs — no visual change expected.

Screenshots

No visual changes intended. All modifications are DOM-semantics only.

AI assistance disclosure

The modifications of this PR — including the semantic-landmark refactor, the layout-preserving CSS cleanup, and the new landmark-structure tests — were made with the assistance of Claude Opus 4.7.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.59%. Comparing base (020a3ee) to head (5e080fe).
⚠️ Report is 23 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2026      +/-   ##
==========================================
+ Coverage   93.53%   93.59%   +0.05%     
==========================================
  Files         363      367       +4     
  Lines        5905     6007     +102     
  Branches     1367     1418      +51     
==========================================
+ Hits         5523     5622      +99     
- Misses        367      368       +1     
- Partials       15       17       +2     

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[brian-smith-tcril]

This is definitely worth addressing, but I have some concerns with the proposed solution in this PR.

I'd like to hear @kblemel's thoughts on this one.

[brian-smith-tcril]

This feels awkward to me. Without this PR the main-content div doesn't contain the AlertList or CourseTabsNavigationSlot. This seems to be splitting main from the main-content div, which doesn't feel right to me.

[jacobo-dominguez-wgu]

That was i mistake, I have fixed it.