Adds vitest coverage for validateCliPresenceAsync and validateCliAuthAsync,
verifying success paths, spawn-error paths, non-zero exit codes, and that
auth failures emit the expected warning. Pairs with the async/memoized
validation refactor in 442238196 that unblocks the dashboard event loop
on every chat send.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>