ci(cli): add semantic PR workflow

[albert20260301]

Summary

• add the shared semantic pull-request title validation workflow

Impact

This adds release-automation guardrails for pull-request titles. It does not alter CLI behavior or published package contents.

Validation

• make lint
• YAML parsed successfully
• workflow formatting check passed
• git diff --check

[albert20260301]

@francoischalifour could you review this?

I picked you because recent history shows you own the CLI release and semantic-workflow area (notably #55). CI is green. The main review focus is that the shared title guard remains compatible with the release pipeline.

[albert20260301]

@francoischalifour please hold review and close this PR.

The default branch already contains the compliant shared workflow at .github/workflows/semantic-pull-request.yml. This PR instead adds a duplicate legacy workflow using ubuntu-latest and amannn/action-semantic-pull-request@v5, so merging it would reintroduce workflow-policy drift and duplicate title checks. I cannot close PRs under the maintainer policy.