List universal events (price-binary across providers)

Returns Artery-assigned universal events grouping price-binary markets across Polymarket, Kalshi and Hyperliquid HIP-4. Use `min_providers=2` to surface cross-platform clusters only. **Pagination — cursor-based (preferred).** Omit `after` for the first page; pass the previous response's `nextCursor` as `after` for subsequent pages. `nextCursor === null` signals end-of-stream. Cursors encode a stable `(firstSeenAt, universalId)` pair, so inserts mid-pagination cannot cause skipped or duplicated rows. **Legacy `offset=N`** still works for one release but is deprecated — expect `Deprecation: true` and `Sunset: 2026-05-30` headers on responses that include `offset`. Mixing `offset` and `after` returns 400.