feat: add ServiceMonitors and enable metrics scraping

- SeaweedFS: enable -metricsPort=9091 on master/volume/filer, add
  service labels, create ServiceMonitor
- Gitea: enable metrics in config, create ServiceMonitor
- Hydra/Kratos: standalone ServiceMonitors (chart templates require
  .Capabilities.APIVersions unavailable in kustomize helm template)
- LiveKit: add prometheus_port=6789, standalone ServiceMonitor
  (disabled in kustomization — host firewall blocks port 6789)
- OpenSearch: revert prometheus-exporter attempt (no plugin for v3.x),
  add service label for future exporter sidecar

base/data/opensearch-service.yaml

@@ -3,6 +3,8 @@ kind: Service
 metadata:
   name: opensearch
   namespace: data
+  labels:
+    app: opensearch
 spec:
   selector:
     app: opensearch