Waitlist with viral loops

Build a viral waitlist app for a pre-launch product.

Core features:
1. Sign up with email, get a spot number
2. Move up the list by sharing a unique link (each signup = -1 position)
3. Milestone rewards (early access, swag) at rank 100/50/10
4. Admin: export, invite in batches, close the waitlist

Data: signups, referrals, invites.
Must-haves: OG image showing user's rank, anti-abuse on referrals.