feat: check if PR title conforms to Conventional Commits

[lsorber]

Changes:

1. Add PR title validation to the root repo.
2. Add PR title validation to the Cookiecutter template, conditional on Conventional Commits being enabled.
3. Add PR title validation to the Copier template, conditional on Conventional Commits being enabled.

Partially addresses #267.

EDIT: I experimented with GitHub Repository Settings and the .github/settings.yml below, but it's apparently quite flakey (cf. repository-settings/app#967) and also a security risk. It appears it's probably best to just set these settings manually after setting up a repo.

repository:
  default_branch: main
  allow_merge_commit: false
  allow_rebase_merge: false
  allow_squash_merge: true
  squash_merge_commit_title: PR_TITLE
  squash_merge_commit_message: PR_BODY
  delete_branch_on_merge: true

branches:
  - name: main
    protection:
      required_pull_request_reviews:
        required_approving_review_count: 1
        dismiss_stale_reviews: false
        require_code_owner_reviews: false
        dismissal_restrictions: null
        bypass_pull_request_allowances: null
        require_last_push_approval: false
      required_status_checks: null
      required_conversation_resolution: true
      required_signatures: true
      required_linear_history: true
      enforce_admins: null
      restrictions: null

[Copilot]

Pull Request Overview

This PR introduces PR title validation to the repository and its templates to ensure that commits follow Conventional Commits. The changes include:

• Adding a new GitHub Actions workflow (pr.yml) in the root repository.
• Adding a conditional pr.yml workflow to the Cookiecutter and Copier templates.
• Conditionally removing the pr.yml file from the generated project when Conventional Commits are not enabled.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
{{ cookiecutter.__project_name_kebab_case }}/.github/workflows/pr.yml	Adds a workflow to validate PR titles using uvx and commitizen.
template/{% if ci == 'github' %}.github{% endif %}/workflows/{% if with_conventional_commits %}pr.yml{% endif %}.jinja	Provides a template for the PR workflow conditional on Conventional Commits being enabled.
hooks/post_gen_project.py	Modifies project generation to remove the pr.yml workflow if Conventional Commits are not enabled.
.github/workflows/pr.yml	Adds a workflow to validate PR titles in the repository.

[PGerardi]

Validated the changes https://github.com/superlinear-ai/my-project/actions/runs/17588466127, works like a charm 🎉

[PGerardi]

LGTM