add arrstack oauth app + per-app access groups

Add the Authentik OIDC application that fronts the arrproxy media front door
at arrstack.unkin.net, plus the per-app entitlement groups arrproxy reads from
the user's groups claim to decide which backends (sonarr/radarr/prowlarr) a
user may reach.

- config/providers_oauth2/arrstack.yaml: confidential oauth2 client
  client_id=arrstack, litellm-style auth/invalidation flows, client_secret
  from Vault kv kubernetes/namespace/arrstack/default/oauth-credentials,
  openid/email/profile scopes, redirect https://arrstack.unkin.net/oauth2/callback,
  launch https://arrstack.unkin.net/. The module always attaches the estate's
  hierarchical ak_groups scope mapping, so the front door emits the groups claim.
- config/permissions/akP-arrstack-user.yaml: front-door gate (application: arrstack).
- config/permissions/akP-arrstack-{sonarr,radarr,prowlarr}.yaml: per-app
  entitlements, unbound (no application) so they only surface in the ak_groups
  claim for arrproxy to authorize backends.
- config/roles/akR-arrstack-user.yaml: full media role nesting all four.
- akR-global-admin: also nests the arrstack front door + all per-app perms.

config/roles/akR-arrstack-user.yaml

@@ -0,0 +1,10 @@
+# Role akR-arrstack-user (name = filename): full media access. Nests the
+# arrstack front-door permission plus every per-app entitlement, so a member can
+# log in at the front door and arrproxy will allow sonarr, radarr and prowlarr.
+# For narrower access, assign the individual akP-arrstack-<app> permission groups
+# (together with akP-arrstack-user for the door) to a user directly instead.
+permissions:
+  - akP-arrstack-user
+  - akP-arrstack-sonarr
+  - akP-arrstack-radarr
+  - akP-arrstack-prowlarr

config/roles/akR-global-admin.yaml

@@ -4,3 +4,9 @@ permissions:
   - akP-argocd-admin
   - akP-rancher-admin
   - akP-litellm-admin
+  # arrstack has no admin tier (it is a proxy front door); grant global admins
+  # the front door plus every per-app entitlement so they reach all media apps.
+  - akP-arrstack-user
+  - akP-arrstack-sonarr
+  - akP-arrstack-radarr
+  - akP-arrstack-prowlarr