- Test KBSettings required fields (base_path, archive_path)
- Test KBSettings optional fields with defaults
- Test secret fields (hf_token, zhihu_cookie) as SecretStr
- Test missing required fields raises ValidationError
- Test get_settings returns singleton via lru_cache
- Test env vars with KB_ prefix are read
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>