Resolve all 374 ruff errors across 36 Python files (E501, E702, E722,
E741, F821, F841, invalid-syntax) bringing `ruff check .` to zero
errors repo-wide with line-length=100.
Rewrite CI workflow to use uv for dependency management, whole-repo
`ruff check .`, py_compile syntax gate, and merged python-tests job.
Add pyproject.toml with ruff config and uv dependency groups.
CI structure proposed by hcm444.
