- Import Header, Depends, Security from fastapi
- Add verify_api_key dependency: reads API_KEY env var, checks X-API-Key
header, raises HTTP 401 if key mismatch; fail-open if env var not set
- Apply Depends(verify_api_key) to all 14 non-health endpoints
- /health endpoint remains unauthenticated for liveness probes
- Mark task 3.2 as complete in tasks.md
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>