Interesting! I built something similar — Echobell (https://echobell.one). Beyond push notifications, it also supports actual phone call alerts, which is useful when you really can't miss something (e.g., server down at 3am). Also has email-to-notification and channel sharing for teams. Worth a look if you need that extra layer.
Cool escalation chain! If you just need the "webhook → iOS phone call" part without the full agent stack, Echobell (https://echobell.one) does exactly that — one iOS app, no server setup. Also works with repeated-call silent bypass.
If you're using Grafana for monitoring, you might also want to get those alerts as actual phone calls on iOS — Echobell (https://echobell.one) takes your Grafana webhook and turns it into a push notification or even a phone call that bypasses silent mode.