add pod dependency management via Kyverno init container injection

Kyverno ClusterPolicy reads dependency.kyverno.io/wait-for annotation
and injects busybox init containers that block until each dependency
is reachable (nc -z). Annotations added to 18 stacks (24 deployments).

Includes graceful-db-maintenance.sh script for planned DB maintenance
(scales dependents to 0, saves replica counts, restores on startup).

stacks/platform/modules/monitoring/grafana_chart_values.yaml

@@ -18,6 +18,8 @@ topologySpreadConstraints:
     labelSelector:
       matchLabels:
         app.kubernetes.io/name: grafana
+podAnnotations:
+  dependency.kyverno.io/wait-for: "mysql.dbaas:3306"
 podDisruptionBudget:
   maxUnavailable: 1
 persistence: