Jellyfin moves to Authentik SSO via jellyfin-plugin-sso (OIDC), keeping
native clients on Jellyfin local/API auth. Adds the oauth2 provider and
application for jellyfin.k8s.syd1.au.unkin.net plus the akP permission
groups gating access, wired into the standard-user and global-admin
roles per the two-tier RBAC model.
- Adds providers_oauth2/jellyfin.yaml: confidential client, secret read
from kv/kubernetes/namespace/jellyfin/default/oauth-credentials,
redirect URIs for the SSO plugin callback paths
- Adds akP-jellyfin-admin and akP-jellyfin-user bound to the app
- Nests akP-jellyfin-user under akR-standard-user and
akP-jellyfin-admin under akR-global-admin
