Connect Lambda to Atlas

[Alexandrbig1]

Priority: High
Difficulty: Medium

---

Description:
Configure AWS Lambda to connect to MongoDB Atlas by adding the MONGODB_URI as an environment variable (sourced from GitHub Secrets). Implement "warm start" optimization for the database connection to reduce cold start latency.

Acceptance Criteria:

• Lambda function uses MONGODB_URI from environment variables
• Database connection is optimized for warm starts
• GET /health/db endpoint returns { ok: true } when the DB is active