Migrate releases to Release Please #126

🤖 [rubykatzen/baseline]:

Goal

Replace the local releaser CLI flow with Google Release Please. The proposed version, changelog, and file changes are reviewed in a GitHub release pull request; merging that pull request is the explicit release action.

Scope

This configures the release lifecycle of Baseline itself. Release automation remains opt-in for consuming repositories: Baseline does not export a shared release workflow or require Release Please through repository policy or embedded fragments.

Implemented

• Pull request titles follow Conventional Commits and are validated from trusted main through pull_request_target.
• Repository policy uses squash-only merges and the pull request title as the complete squash commit message.
• Dependabot produces compatible chore(deps): pull request titles.
• Release Please uses the Ruby strategy and is bootstrapped from v0.9.0.
• A repository-scoped fine-grained PAT is available as RELEASE_TOKEN, allowing generated pull requests to trigger required CI.
• Release Please updates the gem version, changelog, lockfile, pre-commit references, example configuration, and README references.
• The release workflow publishes rubykatzen-baseline to RubyGems after creating the GitHub Release.
• The release workflow advances the floating v0 and v0.x tags used by consumers.
• The old prepare/publish workflows, pre-commit revision bump action, and local releaser flow were retired.
• Release documentation now describes the GitHub-native flow.
• Bundler lockfile checksums were disabled to avoid Release Please's local path gem checksum bug (fix: disable Bundler lockfile checksums #134).
• Changelog linting was aligned with Release Please output (fix: align changelog with Release Please formatting #135).
• Release Please lifecycle labels were disabled; release PR header, footer, and future title format were simplified.
• The first generated release PR, chore: release 0.10.0 #133, proposes v0.10.0 and passes all required checks.

Remaining

• Merge chore: release 0.10.0 #133 manually.
• Confirm that the merge creates GitHub Release and tag v0.10.0.
• Confirm that rubykatzen-baseline 0.10.0 is published to RubyGems.
• Confirm that floating tags v0 and v0.10 point to the released commit.
• Close this issue after the complete release path is verified.

Done when

Release PR #133 is merged and produces the GitHub Release, RubyGems publication, and floating tags without running a local release command.

🚀 📦 ✅