fix: keep /admin reachable while setup is required (#392)

The root layout replaced the entire app with the SetupScreen whenever
the config was incomplete (missing gallery.yaml or Immich credentials)
— including /admin, which lives under the same root layout. That locked
users out of the very tool that fixes an incomplete configuration.

The middleware now forwards the request pathname via an x-pathname
header, and the root layout skips the setup screen for admin paths, so
/admin renders normally (login when ADMIN_PASSWORD is set, the
enable-hint otherwise) while every other route keeps showing the setup
instructions.

Fixes #326

Co-authored-by: ralksta <ralksta@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

middleware.ts

@@ -23,6 +23,9 @@ export function middleware(request: NextRequest) {
 
   const requestHeaders = new Headers(request.headers);
   requestHeaders.set('x-nonce', nonce);
+  // Layouts cannot read the request URL; the root layout needs the pathname
+  // to keep /admin reachable while the app is in setup mode.
+  requestHeaders.set('x-pathname', request.nextUrl.pathname);
   requestHeaders.set('Content-Security-Policy', cspDirectives);
 
   const response = NextResponse.next({