Add experimental server alerts and webhook notifications

Server-side alerting for Docker/container/stack health with Discord,
Slack, Teams, ntfy, Gotify, Telegram, and generic webhooks. Settings
tab, client cache, and backup/restore coverage; marked experimental.

server/services/events.js

@@ -6,6 +6,7 @@ import { docker, extractVolumesList } from './docker.js'
 import { peers } from '../core/peer-registry.js'
 import { Pushes } from '../../shared/protocol.js'
 import { broadcastContainers } from '../handlers/containers.js'
+import { onDockerEvent } from './alerts.js'
 import logger from '../utils/logger.js'
 
 let dockerEventStream = null
@@ -93,6 +94,13 @@ async function openEventStream() {
             data: event,
           })
 
+          // Server-side alerting (webhooks) — independent of connected clients
+          try {
+            onDockerEvent(event)
+          } catch (e) {
+            logger.debug('alerts onDockerEvent error', { error: e?.message })
+          }
+
           // Do not rebroadcast the full list on every exec_*/health_status event —
           // that thrashed clients (rows flicker / disappear on each refresh).
           if (event.Type === 'container') {