arrstack: run sonarr/radarr/prowlarr active-active on shared Postgres (#arrstack)

Convert the three *arr apps from single-replica upstream LinuxServer/SQLite to
our -unkin2 forks running active-active (replicas 3) on a shared CNPG Postgres
cluster.

- new apps/base/arrstack/postgres/: CNPG Cluster arrstack-postgres (3 instances,
  3 managed login roles sonarr/radarr/prowlarr, throwaway initdb owner), per-app
  Database CRDs (<app>-main), cephrgw backup bucket + nightly ScheduledBackup,
  and 3 VaultStaticSecrets syncing the <app>-db role credentials.
- per app: image -> docker-internal/<app>:v<base>-unkin2; replicas 3 +
  RollingUpdate; drop the apikey-init initContainer + PUID/PGID/TZ; run the
  binary directly with -nosingleinstancecheck; env from a new ConfigMap plus
  Postgres user/password and the API key from Secrets; /config PVC -> RWX
  cephfs-raid5-retain (shared).

apps/base/arrstack/radarr/configmap.yaml

@@ -0,0 +1,24 @@
+---
+# Non-secret env for the -unkin2 fork. The fork reads Servarr config from
+# Radarr__<Section>__<Key> env (no config.xml edits, no s6/PUID). Postgres wiring
+# points every replica at the same shared DB (arrstack-postgres-rw / radarr-main);
+# Auth__Method=External defers UI auth to arrproxy/oauth2-proxy; Server__UrlBase
+# keeps the /radarr prefix so arrproxy path-routing works; App__InstanceName is
+# identical across replicas (shared session-cookie name). User/Password/ApiKey
+# come from Secrets (see deployment.yaml), not here.
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: radarr-env
+  namespace: arrstack
+data:
+  Radarr__Postgres__Host: arrstack-postgres-rw.arrstack.svc.cluster.local
+  Radarr__Postgres__Port: "5432"
+  Radarr__Postgres__MainDb: radarr-main
+  Radarr__Log__DbEnabled: "false"
+  Radarr__Auth__Method: External
+  Radarr__Auth__Required: DisabledForLocalAddresses
+  Radarr__App__InstanceName: Radarr
+  Radarr__Server__Port: "7878"
+  Radarr__Server__UrlBase: /radarr
+  Radarr__Update__Mechanism: External