One-shot bootstrap that installs non-Python deps (node, browser,
ripgrep, ffmpeg) via ensure_dependency(), then runs setup if no
provider is configured. Closes the gap between `pip install` and
the full user-facing experience.
Also fixes 3 pre-existing test regressions caused by earlier commits:
- test_recommended_update_command: mock detect_install_method for git env
- test_check_for_updates_no_git_dir: now falls back to PyPI, not None
- test_plist_path_includes_node_modules_bin: skip when dir absent
