feat(waitlist): add pre-launch waitlist module (types, repo, routes)
- Create waitlist/types.ts: WaitlistEntryDoc, Zod schemas for join/status/unsubscribe/admin
- Create waitlist/repository.ts: full CRUD, dedup by emailNormalized, position assignment, stats
- Create waitlist/routes.ts: 5 public endpoints + 7 admin endpoints with role guard
- Add waitlist container to cosmos-init.ts (+ 13 previously missing containers)
- Add dispatchWaitlistJoined webhook to webhooks.ts
- Register waitlistRoutes in server.ts
- Public: join, check status, count, config, unsubscribe
- Admin: list, stats, get, update, delete, batch invite, CSV export
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