Implement idempotent escrow operations

[kimanicode]

Summary

Implements idempotent escrow command execution and reconciliation for the Stellar/Trustless Work escrow integration.
closes #109

Changes

• Added persisted escrow_operations and escrow_operation_audit schema/index definitions.
• Added escrow operation lifecycle handling with:
  • database-enforced idempotency keys
  • deterministic payload hashes
  • resumable submission, confirmation, and projection stages
  • bounded exponential backoff
  • terminal failure handling
  • reconciliation against on-chain/indexed escrow state
  • audit entries for lifecycle and replay/reconcile actions
  • operation age, retry count, and reconciliation failure metrics
• Extended scripts/replay-escrow.mjs with a reconcile mode.
• Added a read-only escrow operation status API.
• Extended escrow hooks with operation status helpers.
• Split indexer event identity helpers into a small shared module to avoid unnecessary decoder imports in escrow projection.
• Added backend tests for idempotency, state transitions, retry/backoff, reconciliation, confirmation failure, and crash recovery.

Verification

node --test tests/backend/escrowOperations.test.mjs tests/backend/escrowIndexer.test.mjs
1..10
# tests 10
# suites 0
# pass 10
# fail 0
# cancelled 0
# skipped 0
# todo 0