fix(infra): use platform node pool for MBP-10 download job

The cluster only has a 'platform' pool, not 'default'.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

infra/k8s/training/download-mbp10-job.yaml

@@ -38,7 +38,7 @@ spec:
         foxhunt/job-type: data-download
     spec:
       nodeSelector:
-        k8s.scaleway.com/pool-name: default
+        k8s.scaleway.com/pool-name: platform
       imagePullSecrets:
         - name: gitlab-registry
       restartPolicy: Never