Add traefik OAuth2 provider/application and akP-traefik-admin permission

The traefik dashboards (internal + external ingress classes) are being
exposed behind oauth2-proxy; this adds the Authentik side as the
prerequisite.

- Adds config/providers_oauth2/traefik.yaml mirroring arrstack: confidential
  client, client_id traefik, secret from Vault kv
  kubernetes/namespace/traefik-system/default/oauth-credentials,
  openid/email/profile scopes (ak_groups is attached to every oauth2
  provider by the module), strict redirect URIs for
  traefik-internal/traefik-external oauth2 callbacks.
- Adds config/permissions/akP-traefik-admin.yaml bound to the traefik
  application and nests it under akR-global-admin.

config/permissions/akP-traefik-admin.yaml

@@ -0,0 +1,3 @@
+# Permission group akP-traefik-admin (name = filename). Grants admin
+# access to traefik: bound to the traefik application, gating the dashboards.
+application: traefik

config/providers_oauth2/traefik.yaml

@@ -0,0 +1,23 @@
+# OAuth2/OIDC provider + application for the traefik dashboards
+# (traefik-internal / traefik-external on k8s.syd1). An oauth2-proxy in front
+# of each dashboard performs the OIDC login; access is gated on the user's
+# hierarchical ak_groups claim (akP-traefik-admin).
+# client_secret is read from Vault (seeded out of band), never committed.
+name: traefik
+authorization_flow: default-provider-authorization-implicit-consent
+invalidation_flow: default-provider-invalidation-flow
+client_type: confidential
+client_id: traefik
+launch_url: https://traefik-internal.k8s.syd1.au.unkin.net/
+client_secret_vault:
+  mount: kv
+  path: kubernetes/namespace/traefik-system/default/oauth-credentials
+scope_mappings:
+  - goauthentik.io/providers/oauth2/scope-openid
+  - goauthentik.io/providers/oauth2/scope-email
+  - goauthentik.io/providers/oauth2/scope-profile
+redirect_uris:
+  - matching_mode: strict
+    url: https://traefik-internal.k8s.syd1.au.unkin.net/oauth2/callback
+  - matching_mode: strict
+    url: https://traefik-external.k8s.syd1.au.unkin.net/oauth2/callback

config/roles/akR-global-admin.yaml

@@ -4,6 +4,7 @@ permissions:
   - akP-argocd-admin
   - akP-rancher-admin
   - akP-litellm-admin
+  - akP-traefik-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