feat(alerts): add liquidation imminent channel with rate-limit and we…

[yunus-dev-codecrafter]

…bhook support

closes #59

Summary

Implement high-priority liquidation alert channel that triggers when any subscribed user's health factor drops below 1.05, regardless of their configured threshold. This feature includes:

• New "LIQUIDATION IMMINENT" notification template for critical HF alerts
• Rate-limited notifications (maximum once per 6 hours per user) to prevent alert fatigue
• Optional webhook POST capability that executes in parallel with email notifications
• Background cron job that continuously monitors user health factors

Changes:

• alerts/src/email.ts: Added sendLiquidationAlert() function with new template
• alerts/src/index.ts: Integrated HF monitoring cron job with rate-limiting and optional webhook support

Related Issue

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Notes for Reviewers

Key Implementation Details:

1. Rate Limiting: Uses Redis or in-memory cache to track last alert timestamp per user, ensuring no more than one HF<1.05 alert per 6-hour window.

2. Webhook Integration: Optional LIQUIDATION_WEBHOOK_URL environment variable enables parallel POST requests with user/HF payload, useful for external automation or alerting systems.

3. Cron Frequency: Background job runs at configurable intervals (recommend every 5-10 minutes) to catch HF dips quickly while avoiding excessive database queries.

4. Template Separation: "LIQUIDATION IMMINENT" uses distinct styling/tone from regular threshold alerts to emphasize urgency.

Testing: Manual testing performed on testnet loop. Alerts fire correctly when HF drops below 1.05 and respect the 6-hour rate limit.

Performance Considerations: Cron job is non-blocking and doesn't impact main alert pathway. Webhook requests timeout after 5s to prevent blocking email delivery.

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