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/navigation/page.tsx

@@ -5,10 +5,6 @@ import { StatusCard } from "@/components/admin/dashboard";
 import { db, NavigatorFlatcats, NavigatorPubliccats, Rooms } from "@/lib/db";
 import { canAccess, getAdminContext, PERMS } from "@/lib/permissions";
 
-// 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;
-
 // navigator_flatcats — emulator-owned flat (private-room) categories shown in the
 // navigator.
 type Flatcat = {