Mattermost and Gotify channels, and acknowledging from the phone

Two new notification channels.

Mattermost. Incoming webhook, works on Mattermost Cloud or your own server. Mentions use the server's own username rules, so directory-synced handles like svc.oncall.emea work.

Gotify. Point a channel at your Gotify server with an application token. Priority follows the client scale: 8 for a high-urgency open, 5 for other opens, 3 for a resolve. The incident link is the notification's click URL.

Acknowledging from the notification itself. An ntfy page carries an Acknowledge button, and acknowledging a Pushover emergency page in the Pushover app acknowledges the incident here too. That stops the repeats still going out on other channels. The link is signed, expires after a week, and is tied to the exact episode it was sent for, so a stale alert on a phone cannot silence a later outage.

Docs: notifications.