Migrate build system to uv with CI/CD pipelines

[Copilot]

Replaces legacy setup.py with a pyproject.toml (hatchling backend) and adds GitHub Actions workflows for PR checks, merge gating, and PyPI publishing via PYPI_API_TOKEN.

Build system

• pyproject.toml with hatchling build backend; all metadata ported from setup.py
• [tool.uv] dev-dependencies block (pytest)
• setup.py removed

CI/CD workflows

Workflow	Trigger	Action
pr.yml	PR → main/master	uv sync + pytest
ci.yml	Push → main/master	uv sync + pytest
publish.yml	v* tag push or Release published	pytest → uv build → PyPI publish

Security

• All jobs scoped to permissions: contents: read; publish job adds id-token: write
• Publish targets a pypi GitHub environment for tag/branch protection
• PyPI upload uses ${{ secrets.PYPI_API_TOKEN }} — must be set under Settings → Secrets → Actions