PixTwins CLI 0.2.1 — cleaner sign-out errors for scripts

Patch release: when the CLI is run while signed out, it now exits with code 1 and reports an authentication error, instead of looking like a server bug. Update with `npm install -g pixtwins@latest`.

• ›Signed-out commands now exit with code 1 (user error) and code AUTH_EXPIRED, not exit 2 (server error)
• ›Scripts can reliably distinguish "you need to log in" from "the server is down"
• ›Backstop heuristics map common error messages (permission denied, not found, network unreachable) to their proper exit codes