* chore(ci): update GitHub Actions to latest major versions
Update actions/cache v4→v5, actions/github-script v3→v7,
actions/stale v9→v10, docker/login-action v3→v4,
docker/setup-buildx-action v3→v4, and docker/metadata-action v5→v6.
The github-script upgrade also migrates Octokit API calls from
github.* to github.rest.* namespace (required since v5).
* fix(ci): address review feedback on GitHub Actions update
Pass github_token to docker/metadata-action@v6 to avoid API rate
limiting. Fix github-script pagination to use the correct Octokit
paginate.iterator pattern (pass endpoint method, not awaited response).
