Test the uninstall command (removal + --purge + --dry-run)

[ropdias]

Follow-up to #5. Builds on the vitest infra and the temp-dir pattern established in src/core/settings.spec.ts.

Scope

src/commands/uninstall.ts. Drive cmdUninstall against a temp dir.

Cases to cover

• Removes only our block: with a tokenline statusLine present (detected via isTokenlineCommand), it deletes just that key, backs up first (settings.json.bak), and leaves unrelated keys intact.
• Foreign statusLine left untouched: a non-tokenline statusLine is not removed.
• No usable settings: missing file or invalid JSON → warns, changes nothing.
• --purge also deletes the installed tokenline.sh; without --purge the script stays.
• --dry-run writes nothing and deletes nothing (both the settings edit and the purge).
• Exit codes behave as expected.

Acceptance

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