feat(reconciliation): integrate Nirium Audit Trail anchor for settlement reports

[Santia2004]

Overview

Integrates cryptographic reconciliation anchoring against the Nirium Audit Trail for JoonaPay settlement reports and ledger batches.

Implementation Details

• Audit Anchor Service (NiriumAuditAnchorService):
  • Consumes generated settlement reports/batches and verifies referenced on-chain transactions (stellar_tx_hash / tx_hash / providerReference).
  • Constructs a deterministic canonical settlement payload with strictly sorted key serialization.
  • Derives domain-separated Nirium-compatible audit CIDs (bafk-nirium-audit-<sha256>).
  • Subscribes asynchronously to settlement.report.generated events without altering fund custody or core ledger mutations.
• Standalone Verification CLI:
  • Added scripts/verify-nirium-reconciliation-anchor.ts to allow compliance teams and external auditors to independently re-derive state hashes and verify ledger parity off-chain.
• Testing & Exports:
  • Added unit test suite covering deterministic CID generation and non-zero fee/volume aggregation.
  • Exported service in ReconciliationModule.

Closes nirium-protocol/nirium#76