[wdm0006]

Closes #161

Adds a scaffold-smoke job (Linux, every PR) running tests/smoke_scaffold.sh: scaffold smoke-lib with create_project.py, then in the generated project uv sync --extra dev, ruff check, ruff format --check, pytest, mypy src, uv build; finally install the wheel into a throwaway venv and import it from the temp dir above the project, asserting the module path is in the venv's site-packages. The stdlib unittest suite and the existing tests job are unchanged.

Real defect found and fixed: the first run failed ruff format --check. The scaffold wrote the __init__.py docstring via !r (single quotes); it now uses json.dumps, giving a double-quoted literal.

Verification

• bash tests/smoke_scaffold.sh passes locally (ruff 0.17.2); unittest discover 62 OK.
• Mutation: unused import os in the template __init__.py -> script fails (F401).
• Mutation: where = ["docs"] -> fails at pytest collection (never reaches the wheel step).
• Mutation: exclude = ["*"] in packages.find (the scaffold uses setuptools, so packages does not apply) -> ruff/pytest/mypy/uv build all pass; only the out-of-tree wheel import fails (ModuleNotFoundError). This is the one that shows the import step guards something.
• Not run: the job on GitHub itself (it runs on this PR).

Tool versions are whatever the scaffold's dev extra resolves; no pins or repo-level lint config added.

Screenshots

n/a — no user-visible change.