Self-Healing Multi-System Webhook Handler

Act as a Lead Backend Developer. Build a Node.js Express webhook listener endpoint that acts as a fail-safe router syncing incoming lead payloads to multiple targets: active database, HubSpot CRM, and Slack alerts channel.

REQUIREMENTS:
- Implement a retry circuit breaker using exponential backoff (max 5 retries).
- If any target fails (e.g. CRM API is down), serialize the payload and push it to a local SQLite 'dead_letter_queue' table.
- Schedule a secondary cron run every 15 minutes to scan the local SQLite queue, attempt re-transmission of queued payloads, and notify sysadmin via email if failure persists beyond 24 hours.