tooling: Add version management (semantic-release + make bump).

[nedseb]

Description

Set up automated and manual version management for the project.

Automated: semantic-release

Configure semantic-release to run in CI on every push to main. It analyzes commit messages and automatically:

• Determines the next version from conventional commits
• Updates pyproject.toml version
• Generates/updates CHANGELOG.md
• Creates a git tag and GitHub release

Release rules:

• feat: → minor bump
• fix:, perf:, refactor:, tooling: → patch bump
• BREAKING CHANGE: in commit body → major bump
• docs:, style:, test:, ci:, chore: → no release

Manual override: make bump

Keep make bump as a fallback for forcing a specific version:

make bump              # patch: v1.0.0 → v1.0.1
make bump PART=minor   # minor: v1.0.1 → v1.1.0
make bump PART=major   # major: v1.1.0 → v2.0.0

Safety checks: must be on main with clean working tree.

Acceptance criteria

• semantic-release configured (.releaserc.json)
• CI workflow .github/workflows/release.yml
• make bump works with PART=patch (default), minor, major
• Safety checks prevent bump on dirty tree or wrong branch
• pyproject.toml version updated automatically
• Document in CONTRIBUTING.md

Related

• PR tooling: Add Makefile and npm hooks for dev workflow. #229 — Makefile setup
• Issue tooling: Add Makefile for common development commands. #201 — Tooling setup