fix(teak): backport sidebar/navigation/breadcrumbs plugin slot changes

[bra-i-am]

Backports two upstream PRs onto the Teak branch to allow the course outline sidebar, sequence navigation, and breadcrumbs to be rendered simultaneously.

Changes included:

• #1716 — migrates sequence navigation into SequenceNavigationSlot
• #1713 — removes the courseware.enable_navigation_sidebar and courseware.always_open_auxiliary_sidebar waffle flags; sidebar is now always visible

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Context

On Teak, the course outline sidebar and breadcrumbs/sequence navigation are mutually exclusive by design — the courseware.enable_navigation_sidebar waffle flag forces operators to choose one or the other. This makes it impossible to show all three elements simultaneously, which is a possible need for deployments that want to provide full course navigation context to learners without sacrificing the outline sidebar.

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⚠️ Known risk

PR #1713 (upstream) also strips the default content from both plugin slots, meaning SequenceNavigationSlot and CourseBreadcrumbsSlot render nothing unless a plugin explicitly injects components into them via env.config.jsx. This creates a regression for any Teak deployment that currently has courseware.enable_navigation_sidebar = false (sidebar off, breadcrumbs and sequence navigation visible): after this backport, the sidebar will be forced on and breadcrumbs/navigation will silently disappear.

Proposed solution (not yet applied)

Restore the default children in both slot components so breadcrumbs and sequence navigation render out-of-the-box without any plugin configuration, matching the behavior operators already rely on:

• CourseBreadcrumbsSlot — restore <CourseBreadcrumbs> as default child
• SequenceNavigationSlot — restore <SequenceNavigation> as default child

Operators who want to replace or disable either component can still do so by setting keepDefault: false in their env.config.jsx. This preserves backward compatibility while keeping the plugin slot extensibility introduced by these two PRs.

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Behavior after this change

	Before	After (Current - without fix of known risk)	After (with fix)
Course outline sidebar	Conditional on waffle flag	Always visible	Always visible
Sequence navigation	Conditional on waffle flag	Hidden (empty slot)	Visible by default via slot
Breadcrumbs	Conditional on waffle flag	Hidden (empty slot)	Visible by default via slot
Customization	Not possible	Via env.config.jsx plugin slots	Via env.config.jsx plugin slots

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Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

@@               Coverage Diff               @@
##             release/teak    #1916   +/-   ##
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  Files                   ?      344           
  Lines                   ?     5732           
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  Hits                    ?     5163           
  Misses                  ?      550           
  Partials                ?       19           

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