Encryption Extensions Persistence

As a system administrator, I want to have the encryption extension list saved in settings.json, So that the configuration is retained without any data loss across application restarts.

Given the user defines a list of extensions to encrypt and saves,
When settings.json is written,
Then the extension list is serialized under a dedicated key without overwriting any other settings.

Given the application is restarted,
When settings.json is read at startup,
Then the full encryption extension list is restored and immediately active for the next backup job.