[ci] Remove release-please Node 20 deprecation warnings

[StatPan]

Summary

• Replace the release-please GitHub Action invocation with a Node 24-compatible CLI flow so release automation no longer emits Node 20 deprecation annotations.

Acceptance Criteria

• .github/workflows/release-please.yml no longer uses googleapis/release-please-action@v4.
• Release PR creation still works.
• GitHub release creation still works.
• The reusable publish pipeline still triggers when a new release is created.
• A workflow validation run completes without the Node 20 deprecation annotation.

[StatPan]

Implementation note: validated the replacement flow locally with actionlint plus release-please CLI dry-runs for both release-pr and github-release.