chore(ingestion): finish ruff swap — nox lint session + skill docs

Three remaining stale-tooling references after Stage 2c:

  - `ingestion/noxfile.py` `lint` session was still calling `black --check`,
    `isort --check-only`, `pycln --diff`. Those tools aren't installed
    anywhere (we dropped them from dev deps). Replace with the ruff
    equivalents that mirror `make py_format_check`.
  - `skills/standards/code_style.md`: stack listed as `black + isort +
    pycln`; line length claimed 88 (black default). Both wrong: stack is
    ruff, line length is 120.
  - `skills/connector-building/SKILL.md`: `make py_format` comment said
    `# black + isort + pycln`. Same swap.

Author: IceS2