Add pytest and Python linting (ruff) to CI (#1637)

* feat: add GitHub Actions workflow for testing and linting Python code

* fix: resolve ruff lint errors in specify_cli

- Remove extraneous f-string prefixes (F541)
- Split multi-statement lines (E701, E702)
- Remove unused variable assignments (F841)
- Remove ruff format check from CI workflow (format-only PR to follow)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: strip ANSI codes in ai-skills help text test

The Rich/Typer CLI injects ANSI escape codes into option names in
--help output, causing plain string matching to fail.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>