Publish release branches with npm series tags

[nhynes]

Summary

• run amber-publish on release branches matching v*.*.x and allow manual dispatch
• tag/cache Docker images by branch name instead of hardcoding main
• publish npm packages from release branches with a non-latest dist-tag like series-0.3

Verification

• node npm/release.mjs spec >/tmp/amber-main-npm-spec.json && node npm/release.mjs matrix --spec /tmp/amber-main-npm-spec.json >/tmp/amber-main-npm-matrix.json
• git diff --check

Runtime validation

• Verified the backported v0.3.x publish workflow completed successfully on run https://github.com/RDI-Foundation/amber/actions/runs/26287350213
• Verified npm shows @rdif/amber dist-tag series-0.3 at 0.3.61 while latest remains 0.4.3