test(cli): verify --cwd redirects config resolution (#997) (#4796)

Adds a CLI test asserting that --cwd changes where config is resolved
from, not just that the directory is valid: the same message is rejected
by the process directory's config but accepted once --cwd points at a
directory whose config allows it.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>