Mobile navigation shows Sign In for authenticated users

[tannerlinsley]

Evidence

PR #1075 replaced the mobile navigation's auth-aware controls with an unconditional link to /login:

• Current default branch: MobileNavigation always renders “Sign In”
• Before Update library landing pages and refresh shared site components #1075: the mobile menu rendered renderAuthControls
• The remaining auth-aware navbar controls are inside the desktop-only container, so they are hidden below the 900px breakpoint.
• NavbarAuthControls already distinguishes loading, signed-out, and signed-in states and exposes Account, My Showcases, Integrations, Admin, and Sign out through AuthenticatedUserMenu.

Impact

Authenticated mobile users see a misleading “Sign In” action. The navbar no longer gives them access to account, showcase, integration, admin, or sign-out actions that were available before #1075.

Proposed direction

Add a mobile presentation to the existing auth-control path and render it in the redesigned utility section. Trigger its existing lazy/auth loading when the mobile menu opens so the signed-out path stays lightweight. Keep capability checks and sign-out behavior in the current components rather than duplicating them in Navbar.tsx.

Alternatives and tradeoffs

• Reuse the current compact avatar dropdown unchanged: smallest code change, but it does not fit the new full-width mobile menu row.
• Render authenticated account actions inline in the mobile menu: clearest mobile UX, but risks duplicating capability and sign-out logic unless NavbarAuthControls owns that presentation.
• Keep the unconditional login link: simplest, but preserves the regression.

Decision needed

@tannerlinsley Please choose whether signed-in mobile navigation should use a full-width account row that opens the existing menu or expose the account actions inline.