chore: validate PR titles with conventional commits

[dustinbyrne]

💡 Motivation and Context

Our changelog automation uses merged PR titles to determine changelog candidates/entries. Enforcing Conventional Commit PR titles across SDK repos keeps titles structured and easier to classify consistently.

💚 How did you test it?

• Parsed the new workflow YAML locally with PyYAML.

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• No changeset/Sampo entry needed for this CI-only change.

[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
.github/workflows/lint-pr.yml:5-8
The `reopened` event type is missing. Without it, reopening a previously closed PR (without editing it) skips title validation, so a PR with a non-conforming title could be merged after a reopen cycle without ever triggering the linter.

```suggestion
    types:
      - opened
      - edited
      - synchronize
      - reopened
```

_{Reviews (1): Last reviewed commit: "chore: validate PR titles with conventio..." | Re-trigger Greptile}