ci: add conventional-commit PR title lint (LAB-451)

[27Bslash6]

Adds the conventional-commit PR-title gate to this release-please repo, matching the one already live on cachekit-io/saas (#247).

Why

This repo is squash-merge-only, so the PR title becomes the squash commit header that release-please parses. Non-conventional titles — notably a LAB-NNN: prefix — are silently skipped: no version bump, no changelog entry, no error. Live example: cachekit-py#228's LAB-381: title starved the SWR release and blocked a downstream consumer (LAB-465). This check fails such titles at PR time instead of one release later.

What

• Dependency-free grep against the standard conventional-commit type set; PR title read via env (not inline ${{ }}) — injection-safe.
• Runs on opened/edited/reopened/synchronize so it can be promoted to a required status check.

Rollout of LAB-451's "what's next" item 5 (extend the saas guard to the other release-please repos: py / ts / rs / core).

Follow-up after merge

Mark conventional-title a required status check in branch protection — a check can't be made required until it has produced a status on main at least once.

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⚙️ Run configuration

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📥 Commits

Reviewing files that changed from the base of the PR and between 5736660 and e68c509.

📒 Files selected for processing (1)

• .github/workflows/pr-title-lint.yml

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch lab-451-pr-title-lint

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