Handle database outages gracefully

[joaoc-dev]

Possible approach:

• Health Check API Endpoint
  Created /api/health endpoint that returns current service status
  Returns structured health data including database connection state
  Uses HTTP status codes (200 for healthy, 503 for unhealthy)

• Custom Error Handling System
  Created lib/errors.ts with comprehensive error classification:
  DATABASE_CONNECTION_ERROR (503) - Connection refused/failed
  DATABASE_TIMEOUT_ERROR (504) - Operation timeouts
  SERVICE_UNAVAILABLE (503) - General service issues

Handle it in the UI by redirecting to service unavailable page.