arrstack: repoint arrproxy oauth2-proxy image off ghcr

ghcr.io/oauth2-proxy/oauth2-proxy does not permit anonymous pulls (its
ghcr token endpoint returns DENIED), so artifactapi's anon-only ghcr
remote returns 401 and the sidecar is stuck in ImagePullBackOff. valkey-io
and other ghcr images work because they issue anon tokens.

Repoint the oauth2-proxy sidecar to the docker-internal local registry,
where the multi-arch v7.15.3 image (mirrored from quay.io, identical
digest sha256:10a11657...) is anon-pullable, restoring the arrproxy front
door.

apps/base/arrstack/arrproxy/oauth2-proxy-deployment.yaml

@@ -62,7 +62,7 @@ spec:
               memory: 64Mi
       containers:
         - name: oauth2-proxy
-          image: artifactapi.k8s.syd1.au.unkin.net/ghcr/oauth2-proxy/oauth2-proxy:v7.15.3
+          image: artifactapi.k8s.syd1.au.unkin.net/docker-internal/oauth2-proxy:v7.15.3
           imagePullPolicy: IfNotPresent
           ports:
             - containerPort: 4180