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/(site)/developers/page.tsx

@@ -1,9 +1,5 @@
 import { ContentCard } from "@/components/public/ui";
 
-// 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;
-
 // Public API documentation. Static, hand-maintained from the routes that
 // actually exist under src/app/api — keep this in sync when endpoints change.