Onboard mediamark to Authentik OIDC

Add an oauth2 provider/application for the mediamark kids-content marking UI,
a permission group gating it, and nest that permission in akR-media-adult.

config/permissions/akP-mediamark.yaml

@@ -0,0 +1,3 @@
+# Permission group akP-mediamark (name = filename). Grants access to mediamark:
+# bound to the mediamark application, gating the kids-content marking UI.
+application: mediamark

config/providers_oauth2/mediamark.yaml

@@ -0,0 +1,25 @@
+# OAuth2/OIDC provider + application for mediamark (the Go web UI for marking
+# media as kids content, served at https://mediamark.unkin.net (external
+# hostname) and https://mediamark.k8s.syd1.au.unkin.net (cluster hostname) in
+# the arrstack namespace). An oauth2-proxy in front of the UI performs the OIDC
+# login with a relative redirect, so both hostnames must be registered; access
+# is gated on the user's hierarchical ak_groups claim (akP-mediamark).
+# client_secret is read from Vault (seeded out of band), never committed.
+name: mediamark
+authorization_flow: default-provider-authorization-implicit-consent
+invalidation_flow: default-provider-invalidation-flow
+client_type: confidential
+client_id: mediamark
+launch_url: https://mediamark.unkin.net/
+client_secret_vault:
+  mount: kv
+  path: kubernetes/namespace/arrstack/default/mediamark-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://mediamark.k8s.syd1.au.unkin.net/oauth2/callback
+  - matching_mode: strict
+    url: https://mediamark.unkin.net/oauth2/callback

config/roles/akR-media-adult.yaml

@@ -2,7 +2,10 @@
 # adult ("fafflix") and kids ("cheeztv") services, so this role nests both
 # per-service entitlements. Membership propagates child -> parent, so a member
 # appears in both permission groups in the hierarchical `ak_groups` claim and the
-# media proxy routes/authorizes them for fafflix and cheeztv.
+# media proxy routes/authorizes them for fafflix and cheeztv. Adults also curate
+# which titles are kids content, so the role nests akP-mediamark for access to
+# the mediamark UI.
 permissions:
   - akP-media-fafflix
   - akP-media-cheeztv
+  - akP-mediamark