CI cross-build fix — post-merge confirmation gate

Tracking the post-merge gate for the multi-arch cross-compile fix (PR forthcoming).

## Closure criteria

- [ ] `pull-node-feature-discovery-build-image-cross-generic` is green on **5 consecutive PRs** against master after merge.
- [ ] Recorded baseline: `nfd-worker --oneshot --no-publish` output from a real `linux/arm64` node, attached as `arm64-baseline.txt` on this issue.
- [ ] (Best effort) For ppc64le and s390x: record a `feature.node.kubernetes.io/cpu-cpuid.*` label list from a real-hardware run if available; otherwise mark as 'qemu-validated only' in release notes.

## Rollback triggers

If any of the criteria fail in the gate window, pick the rollback path documented in the design spec (`.agents/plans/2026-05-15-multiarch-buildx-cross-compile-design.md`):

1. Narrow release scope: set `IMAGE_ALL_PLATFORMS=linux/amd64,linux/arm64` in `scripts/test-infra/push-image.sh`.
2. Per-arch fallback: override `--platform=$TARGETPLATFORM` on the builder stage for the broken arch only.

`git revert` is **NOT** a safe rollback — it reintroduces the QEMU memory-corruption crash class.

## References

- Design (in fork): `.agents/plans/2026-05-15-multiarch-buildx-cross-compile-design.md` (commit `891d63aa0` on `ArangoGutierrez/node-feature-discovery@agents-workbench`)
- Plan (in fork): `.agents/plans/2026-05-15-multiarch-buildx-cross-compile-plan.md`
- Test-infra context: kubernetes/test-infra#37041
- tonistiigi/xx digest: `sha256:010d4b66aed389848b0694f91c7aaee9df59a6f20be7f5d12e53663a37bd14e2`

Start with the design and plan files in the referenced fork, then inspect scripts/test-infra/push-image.sh and the pull-node-feature-discovery-build-image-cross-generic job. Verify the job is green on five consecutive PRs after the merge, attach the arm64 baseline output, and record or explicitly mark the ppc64le and s390x validation status.

Written by the indexing model from the issue text.