arrstack: gate apps on DB via initContainer instead of sync-waves

Per review: drop the ArgoCD sync-wave annotations (their health-gating is
what deadlocked the first deploy) and instead add a wait-for-db init
container to each app that blocks until its own Postgres database+role is
reachable (libpq PG* env, password never in argv). ArgoCD applies
everything at once; the app container only starts once its DB is ready.

apps/base/arrstack/postgres/cnpg_cluster.yaml

@@ -11,11 +11,6 @@ kind: Cluster
 metadata:
   name: arrstack-postgres
   namespace: arrstack
-  annotations:
-    # Wave 1: the per-app <app>-db Secrets (wave 0) must exist first — CNPG reads
-    # them as the managed roles' passwordSecret. ArgoCD gates dependents on the
-    # Cluster's health status.
-    argocd.argoproj.io/sync-wave: "-2"
 spec:
   inheritedMetadata:
     annotations: