ci: add semantic PR title workflow

[albert20260301]

Summary

• add the shared semantic PR title workflow managed by sdk-sync
• enforce Conventional Commit PR titles before squash-merge release automation consumes them

Testing

• not run; workflow-only change

[albert20260301]

@leonkenneth could you review this?

I picked you because Ruby is in your stack. CI is just the new PR-title validation workflow. The review focus is whether adding the shared semantic title check is appropriate for this repo now.