Allow adding SSH hosts without authentication credentials by introducing
a new "none" auth type. This enables users to configure hosts for later
use with SSH agent or manual credential addition.
Changes:
- Add authType "none" to type definitions
- Update frontend form to support "None" authentication option
- Skip credential validation for "none" auth type
- Update backend to accept hosts without credentials
- Add i18n support for English and Chinese
Fixes#278
