Fix docker push unauthorized: mount config.json, not .dockerconfigjson

Confirmed via a direct token request to Harbor's own token endpoint
(same username/password from harbor-robot-dockerconfig) that the
robot account genuinely has push access to homelab/demo-go-app —
Harbor returned a valid token with actions:[pull,push]. So the actual
`docker push` failure ("unauthorized... action: push") wasn't a
permissions problem at all.

Root cause: kubernetes.io/dockerconfigjson secrets are required to
store their data under the fixed key `.dockerconfigjson`. Mounting
the secret without remapping that key meant the file that actually
landed at /root/.docker was named `.dockerconfigjson`, not
`config.json` — the only filename docker's CLI reads for stored
credentials. Docker found nothing there and pushed unauthenticated,
which Harbor correctly rejected. Adds an items: remap so the mounted
file is named config.json.

resources/org/homelab/dind-pod.yaml

@@ -72,3 +72,18 @@ spec:
     - name: docker-config
       secret:
         secretName: harbor-robot-dockerconfig
+        # kubernetes.io/dockerconfigjson secrets store their data under
+        # the fixed key `.dockerconfigjson` (mandated, since that's what
+        # kubelet reads for imagePullSecrets) — without this remap, the
+        # mounted file at /root/.docker is literally named
+        # `.dockerconfigjson`, not `config.json`, which is the only
+        # filename the docker CLI itself ever reads for stored
+        # credentials. Docker found nothing there and silently pushed
+        # unauthenticated, which Harbor correctly rejected as
+        # unauthorized — confirmed the robot account/credentials
+        # themselves were fine the whole time by requesting a push token
+        # directly from Harbor's token endpoint with the same username/
+        # password and getting one back with push access granted.
+        items:
+          - key: .dockerconfigjson
+            path: config.json