muster release v5.18.1

Helm: MusterMCPServerFailed and MusterMCPServerFlapping survive a muster rollout (#1203). Both expressions now aggregate over cluster_id, installation, pipeline, provider, namespace, mcpserver_namespace, mcpserver_name (max by for the state gauge, sum by for the transition counter) instead of carrying the scrape labels pod, instance, container, endpoint, service, job and otel_scope_name into the alert. Before, every rollout ended the old pod’s series – Alertmanager sent RESOLVED – and the new pod’s series started a fresh for window that fired again 20 minutes later: four rollouts in one day produced seven notifications for a single backend that never came back. The alert’s identity is now the MCPServer on a cluster; the for windows, labels and annotations are unchanged, and state is no longer an alert label (both rules only select Failed). The promtool suite covers the series moving from one pod to the next mid-window.