Dashboard should paginate — currently scans only first 20 invoice IDs

[MarcusDavidG]

The dashboard fetches invoices by scanning IDs 1–20 linearly. This won't scale as more invoices are created on-chain.

Better approach: index invoice IDs per creator address via a Stellar Horizon event listener, then fetch only relevant IDs.

Short term: expose a configurable scan range. Long term: event indexer.