ci: enforce conventional commit format on PR titles

[ian-flores]

Summary

• Adds a GitHub Action that validates PR titles follow conventional commit format
• Updates CONTRIBUTING.md and CLAUDE.md to document the requirement

Context

semantic-release was skipping releases because commits weren't following conventional format (e.g., PR #66's "fix tests" instead of "fix: tests").

With this change:

1. PR titles are validated by CI - must start with feat:, fix:, docs:, etc.
2. Combined with squash merge (repo setting), the PR title becomes the commit message
3. semantic-release can then properly analyze commits for version bumps

Checklist

• CI workflow added (.github/workflows/pr-title.yml)
• CONTRIBUTING.md updated with enforcement details
• CLAUDE.md updated with summary
• Manual step required: Enable "Squash and merge only" in repo settings (Settings → General → Pull Requests)

Test plan

• Open a PR with invalid title (e.g., "add feature") - should fail CI
• Open a PR with valid title (e.g., "feat: add feature") - should pass CI

[claude]

Claude finished @ian-flores's task —— View job

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Reviewing PR

• Read review guidelines
• Create pending review
• Get PR diff and analyze changes
• Add inline review comments
• Submit review

Review submitted with feedback on:

• Version pinning suggestion for the GitHub Action
• Minor documentation enhancement idea
• Confirmation that changes follow existing patterns and have no security concerns

Note: I was unable to add inline comments due to permissions, so feedback was included in the review body instead.

[claude]

Review Summary

This PR adds CI enforcement for PR title conventions, which solves a real problem (semantic-release skipping releases due to non-conforming commits). The implementation is solid and follows existing patterns.

What's Good:

• Uses amannn/action-semantic-pull-request@v5, a well-maintained action for this purpose
• Documentation updates in CONTRIBUTING.md are thorough and explain the "why" behind the requirement
• The workflow triggers on appropriate events (opened, edited, synchronize, reopened)
• CLAUDE.md update is appropriately concise

Minor Suggestions:

1. Version pinning (.github/workflows/pr-title.yml:23): Consider pinning to a specific version (e.g., @v5.4.2) with Dependabot for updates. This improves security and reproducibility. The @v5 pattern is acceptable but less secure.

2. Header comment examples (.github/workflows/pr-title.yml:1-10): The examples in the header are helpful. Consider adding one with a scope, e.g., fix(api): fix validation bug to show the optional scope syntax.

Checklist:

• Follows existing CI workflow patterns
• Documentation is clear and actionable
• No security concerns with the changes

Note for merging: The PR description mentions enabling "Squash and merge only" in repo settings. Ensure this is done before relying on this enforcement.