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/admin/layout.tsx

@@ -21,12 +21,9 @@ import { readCsrfCookieToken } from "@/lib/foundation/security";
 import { canAccess, getAdminContext, PERMS } from "@/lib/permissions";
 import { siteSettings } from "@/lib/services/site-settings";
 
-// 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
-export const instant = false;
-
 // Request-time auth, existing CSRF cookie, and optional 2FA gate cannot be
-// statically rendered. Child admin pages inherit this — leaf force-dynamic is redundant.
+// statically rendered. The root layout's Cache Components opt-out
+// (instant = false) covers this route tree — leaf opt-outs are redundant.
 
 export default async function AdminLayout({
 	children,