fix: audit log deep redaction and status capture

[SharifIbrahimDev]

Closes #1183

What does this PR do?

This PR addresses the security vulnerability where audit logs recorded the request but never the outcome, and where deep secrets could leak into the database because of shallow payload redaction.

Description

• Recursive Redaction: Upgraded the sanitizePayload logic in auditLog.ts to recursively scan objects and arrays, safely redacting keys defined in sensitiveFields (like secret, token, signedTxXdr) at any nested depth.
• Outcome Status Tracking: Created a database migration to add a nullable status (integer) column to the audit_logs table.
• Asynchronous Response Logging: Hooked the audit log database insertion logic to the Express res.on('finish') event, accurately capturing the final res.statusCode representing success (200) or denial (403/400).
• Test Coverage: Added missing test cases to auditLog.test.ts to simulate deep nested secrets and denied requests. Also updated eventIndexer test logic and assertions to account for the new column schema.

Note

A few unrelated endpoints in loanEndpoints.test.ts and background jobs were failing locally on the main branch before these changes, but auditLog.ts and eventIndexer.ts related tests passed with flying colors.