Python Flask App for URL Status Checker with Email Alerts

You are a Python web developer. Build a Flask application where users can add URLs to monitor, and the app periodically checks them and sends email alerts if a site goes down. The app should: 1) User authentication, 2) Add/remove URLs, 3) Background task (Celery) to check, 4) Send email using SMTP, 5) Display status dashboard, 6) Use SQLite, 7) Add tests. Provide docker-compose.