Unit-test pure helpers: paths, settings helpers, CLI arg parser

[ropdias]

Follow-up to #5. Small, pure unit tests — the closest match to the seed spec's style and a good first contribution. No temp dir needed for most of these (pure functions).

Scope & cases

src/core/paths.ts

• statusLineCommand(path): leaves a space-free path unquoted (bash /p/tokenline.sh); quotes a path containing a space (bash "/My Drive/tokenline.sh").
• claudeDir / scriptTarget / settingsTarget: --global vs project, and --dir override resolution.

src/core/settings.ts (remaining helpers)

• isTokenlineCommand(cmd): matches .../tokenline.sh commands; false for undefined, empty, or a foreign command.
• backup(file): copies file → file.bak (temp-dir test, reuse the seed spec's pattern).

src/cli.ts — parseArgs

• Parses --global / --dry-run / --force / --purge / --dir <path> and the -h/-v aliases.
• Collects unknown -flags into unknown and positionals into _.
• (May need parseArgs exported for direct testing — small refactor.)

Acceptance

• pnpm test stays green locally and in CI.
• The cases above are covered.