Adds /admin, /admin/requests, /admin/quarantine, /admin/users routes to
the ShellRoute (so PlayerBar persists). Redirect closure refuses any
/admin path when user.isAdmin is false. Server-side RequireAdmin
middleware remains the actual authority — this is UX.
Screens land in subsequent commits; this intermediate state won't build
until task 8/9 lands the AdminLandingScreen and the missing siblings
are stubbed out by task 11/13/16.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
bvandeusen
dfc08650e7