Configurable Encryption Extensions

As a user, I want to define the list of file extensions to encrypt in the general settings, So that I control precisely which file types are passed to CryptoSoft during a backup.

Given the user opens the encryption section in the general settings,
When the panel renders,
Then they can add, edit, and remove individual file extensions (e.g., .docx, .pdf) from the list.

Given the user saves an updated encryption extension list,
When the next backup job runs,
Then only files matching the updated list are passed to CryptoSoft; all others are copied in plain text.

Given the user clears the entire encryption extension list,
When a backup job runs,
Then no files are encrypted and CryptoSoft is never invoked during that job.

Given the user types an extension without the leading dot (e.g., pdf instead of .pdf),
When the input is validated on save,
Then the application automatically normalizes it to the correct format (.pdf) before persisting it.