List subscribable webhook events

List the catalog of event types that can be subscribed to, each with a label and a description of what it carries. Only content.recalled and content.restored events are actually sent today; other listed events are not yet emitted.

Notes.

• data per event — screen.offline: screenId, screenName, status, nodeId, nodeName, lastSeenAt, upForSec, scheduledOff. screen.online: screenId, screenName, status, nodeId, nodeName, lastSeenAt, offlineSince, offlineForSec. approval.requested: requestId, contentKind, contentId, contentName, nodeId, nodeName, requestedById, requestedByName, requestedAt, note. approval.decided: the same plus decision (approved | rejected | withdrawn), decidedById, decidedByName, decidedAt, decisionNote. emergency.started: emergencyId, headline, body, severity, contentKind, contentId, scopeKind, scopeNodeId, scopeName, screenCount, triggeredById, triggeredByName, triggeredAt, expiresAt, templateId, templateName. emergency.cleared: the same plus clearedAt, clearedById, clearedByName, reason (cleared | expired | replaced | content-deleted). content.recalled: kind, id, name, reason, recalledBy. content.restored: kind, id, name.
• screen.offline is sent once per outage, when Brix marks the screen offline (seconds after a socket drop, up to 45 minutes for a screen that reports only by heartbeat). A screen that drops again before it is back is the same outage. screen.online follows when it reports again, within about 5 minutes.