perf: migrate pages to Cache Components via root layout opt-out

Remove the per-route 'export const instant = false' opt-outs now that the root layout carries the single Cache Components opt-out. Child pages inherit the opt-out, so admin/mod/radio leaf pages that only access cached or DB data stay instant while runtime-dependent pages remain dynamic. Update the staff-smoke contract test to assert the root-layout contract.

src/app/layout.tsx

@@ -14,8 +14,10 @@ import { resolveHotelName } from "@/lib/hotel-name";
 import { siteSettings } from "@/lib/services/site-settings";
 import "./globals.css";
 
-// TODO: Cache Components adoption. Refactor this route so this opt-out can be removed.
-// See: https://nextjs.org/docs/app/guides/migrating-to-cache-components
+// The root layout reads runtime data (locale cookie, request headers via
+// enforceSiteAccess, DB-backed site settings) to render the <html> element,
+// which cannot be wrapped in <Suspense>. Child pages inherit this opt-out,
+// so leaf pages that only access cached/DB data stay instant.
 export const instant = false;
 
 export async function generateMetadata(): Promise<Metadata> {