victoria-metrics: pin back to chart 0.77.0 after a failed 0.91.2 upgrade

The 0.91.2 bump had been sitting in Git unapplied because the app could not
generate manifests. Once the values path was fixed it applied, and Grafana
crash-looped on "Datasource provisioning error: data source not found".
Rolled back; Grafana and all 35 VMRules are healthy again on 0.77.0.

0.91.2 also moves the default dashboards and rules out of the Helm render
into a runtime sync-job, so upgrading needs a values migration and a
verified datasource config rather than a version bump.

infra/argocd/applications/victoria-metrics-application.yaml

@@ -8,7 +8,13 @@ spec:
   sources:
     - repoURL: https://victoriametrics.github.io/helm-charts/
       chart: victoria-metrics-k8s-stack
-      targetRevision: 0.91.2
+      # Pinned at 0.77.0. 0.91.2 was tried on 2026-08-29 and rolled back:
+      # Grafana crash-looped on "Datasource provisioning error: data source
+      # not found". The chart also moves dashboards and the 35 default VMRules
+      # out of the Helm render and into a runtime sync-job, so the upgrade
+      # needs a values migration and a verified datasource config, not a
+      # version bump.
+      targetRevision: 0.77.0
       helm:
         # Release name kept short to avoid label length >63 chars on alertmanager StatefulSet pods
         releaseName: vm