feat(logger): add centralized sensitive field redaction to logs (#691)

[ravendevhub]

Summary

Resolves #691 by implementing a centralized redaction policy and sanitizer engine (listener/src/utils/redact.ts) ensuring API keys, passwords, webhook URLs, bearer tokens, and Stellar secret keys are systematically sanitized before being emitted to log outputs.

Changes

1. Redaction Engine (listener/src/utils/redact.ts):
   • Detects and masks sensitive object keys (password, secret, authorization, api_key, webhook_url, etc.).
   • Redacts string patterns: Bearer tokens (Bearer [REDACTED]), Discord webhooks (https://discord.com/api/webhooks/[REDACTED_WEBHOOK_URL]), and Stellar secret keys (S[REDACTED_STELLAR_SECRET_KEY]).
   • Recursively sanitizes Error instances, nested causal chains, and stack traces.
2. Logger Integration (listener/src/utils/logger.ts):
   • Automatically passes message strings and metadata through redactSensitiveData before formatting.
3. Tests & Documentation:
   • Comprehensive test suite in redact.test.ts verifying object, string, error, and circular reference redactions.
   • Specification documented in docs/SENSITIVE_FIELD_REDACTION.md.

Acceptance Criteria

• Sensitive fields have a defined redaction policy.
• Redaction is applied consistently.
• Error logging does not bypass the policy.
• Tests verify that representative secrets are not emitted.