fix: alert acknowledgment not persisting - map update was missing

The AcknowledgeAlert function was modifying the alert pointer but not writing
it back to the activeAlerts map. Since Go maps store values (not references),
the acknowledged state wasn't being persisted. Fixed by adding the map update
after modifying the alert properties.

internal/alerts/alerts.go

@@ -933,6 +933,9 @@ func (m *Manager) AcknowledgeAlert(alertID, user string) error {
 	now := time.Now()
 	alert.AckTime = &now
 	alert.AckUser = user
+	
+	// Write the modified alert back to the map
+	m.activeAlerts[alertID] = alert
 
 	return nil
 }