fix: send notifications for critical alerts restored from disk after restart

addresses #471

when pulse restarts (service restart, container restart, etc), active alerts
are loaded from disk but notifications were never sent for these restored
alerts. this caused users to miss critical ongoing alerts that existed before
the restart.

the issue was particularly noticeable with memory alerts on VMs - if a VM's
memory was genuinely high and an alert was created, then pulse restarted, the
alert would show in 'Active Alerts' but no webhook notification would be sent.
however, manually creating a 'fake' alert by lowering thresholds would work
because those are new alerts.

fix: now sends notifications for restored critical alerts that started within
the last 2 hours. adds a 10-second delay after restart to allow the system
to stabilize before sending notifications. warning-level alerts are not
re-notified to avoid spam on restart.

internal/alerts/alerts.go

@@ -2268,6 +2268,23 @@ func (m *Manager) LoadActiveAlerts() error {
 
 		m.activeAlerts[alert.ID] = alert
 		restoredCount++
+
+		// For critical alerts that are still active after restart, send notifications
+		// This ensures users are notified about ongoing critical issues even after service restarts
+		// Only notify for alerts that started recently (within last 2 hours) to avoid spam
+		if alert.Level == AlertLevelCritical && now.Sub(alert.StartTime) < 2*time.Hour {
+			// Use a goroutine and add a small delay to avoid notification spam on startup
+			if m.onAlert != nil {
+				go func(a *Alert) {
+					time.Sleep(10 * time.Second) // Wait for system to stabilize after restart
+					log.Info().
+						Str("alertID", a.ID).
+						Str("resource", a.ResourceName).
+						Msg("Sending notification for restored critical alert")
+					m.onAlert(a)
+				}(alert)
+			}
+		}
 	}
 
 	log.Info().