V.C. Billingsley6/12/2026, 12:42:21 AM

- Add components/app-shell.tsx: viewport-locked floating card (FLOATING_CARD_STROKE)
  with AppSiteChrome pinned at top, an optional static sub-nav slot, and a single
  internally-scrolling content area — the same frame the dashboard uses.
- RepositoryShell: render inside AppShell with a static RepositoryTabs sub-bar;
  drop the collapsing scroll header and the full/contained layout preference.
- Settings (/settings, /[username]/settings) and the repository settings layout,
  the profile page, and repositories/new now render inside AppShell.
- Remove the now-unused RepositoryScrollHeader and SiteScrollHeader, and the
  dead layout-preference toggle from account settings.

Marketing/auth/onboarding and the immersive PR-Files layout are intentionally
left unframed.

Parentc8462e2