ci: add lint + smoke workflow

[bgorzelic]

What

Adds .github/workflows/ci.yml — a minimal CI workflow that runs on pushes to main and on all pull requests.

Checks

1. Install — Python 3.11, pip install -e . (verifies packaging metadata and dependency resolution)
2. Lint — ruff check . using the existing [tool.ruff] config in pyproject.toml
3. Smoke import — python -c "import skyforge"
4. CLI — skyforge --help (verifies the Typer entry point loads)

Verification

All steps run locally against this branch:

• ruff check . → All checks passed
• pip install -e . → clean install
• import skyforge and skyforge --help → OK

No ruff config was added — the repo's existing pyproject.toml ruff section passes as-is.