Allow to send notifications when UK database is down

📑 I have found these related issues/pull requests Somewhat related as a topic to #6046 🛡️ Security Policy • I have read and agree to Uptime Kuma's [Security Policy]( 📝 Description Tested on external Mariadb, perhaps the same issue on others. When the uptime kuma database (it's own database) is not available, UK stops functioning completely. It does not send a notification to inform UK itself is having issues. 👟 Reproduction steps 1. Run UK with an external MariaDB database 2. Take down the database. 3. Verify UK became unresponsive, and no notifications are triggered. 👀 Expected behavior UK will send a notification to all notification channels that UK itself is having issues/is down. 😓 Actual Behavior No notifications were sent 🐻 Uptime-Kuma Version 2.0.2 💻 Operating System and Arch Debian Trixie (13.2), x86_64 Kernel Debian 6.12.57-1 (2025-11-05) x86_64 🌐 Browser not relevant 🖥️ Deployment Environment • Runtime Environment: - Docker:…