Keep the waitlist schema with the control worker that reads it
Moves the waitlist migration next to the control worker so the local backend build works again.
The site rebuild removed apps/marketing/migrations, but the control worker still binds WAITLIST_DB for beta access, and its wrangler.jsonc pointed at the deleted folder. bun run backend:build failed with ENOENT.
The schema file 0001_create_waitlist_signups.sql is now at workers/control/waitlist-migrations/, and scripts/build-local-backend.mjs and scripts/local/backend.mjs copy it from there. The backend builds and serves again.
Evidence
No screenshot: Build and config fix; nothing to screenshot.