Add optional password requirement for SSH sessions (Issue #118)

Users can now choose whether to require a password when saving SSH sessions.
A new "Require Password" toggle has been added to the password authentication
tab, allowing sessions to be saved without entering a password when disabled.

- Add requirePassword boolean field to SSH host schema (defaults to true)
- Update form validation to conditionally require password based on setting
- Add "Require Password" toggle with description in Host Manager UI
- Update all backend SSH routes to handle requirePassword field correctly
- Add translations for new UI elements in English and Chinese
- Maintain full backward compatibility with existing hosts

Resolves #118

src/locales/en/translation.json

@@ -502,6 +502,8 @@
     "upload": "Upload",
     "authentication": "Authentication",
     "password": "Password",
+    "requirePassword": "Require Password",
+    "requirePasswordDescription": "When disabled, sessions can be saved without entering a password",
     "key": "Key",
     "credential": "Credential",
     "selectCredential": "Select Credential",