Add PyPI publishing workflows and switch to uv_build backend

[zachgiordano]

Adds a release/publish pipeline so new versions can be cut to PyPI, mirroring griptape-nodes. The last published version (0.1.1) is behind main and missing the /api endpoint-prefix change.

Changes

• publish.yml — on a published Release (or manual dispatch), runs make check, then uv build + uv publish. Docker jobs omitted (no images); publish matrix pinned to 3.12.
• stable-release.yml — on v* tag, creates a GitHub Release.
• version-bump-on-release.yml — on release/** push, cherry-picks the version bump back to main via PR.
• Makefile — adds the version/* targets the flow depends on.
• Build backend — hatchling → uv_build (flat layout, so module-root = ""; the gitignored generated/ scratch dir is excluded from the build).
• Version — 0.1.0 → 0.2.0 so the next publish lands above 0.1.1.

Required secrets

• PYPI_TOKEN — publish to PyPI.
• RELEASE_PAT — release + PR creation.