Removed obsolete handlers from roles (VirtualBox, backup-to-USB, OpenLDAP)
and introduced an integration test under tests/integration/test_handlers_invoked.py
that ensures all handlers defined in roles/*/handlers are actually notified
somewhere in the code base. This keeps the repository clean by preventing
unused or forgotten handlers from accumulating.
Ref: https://chatgpt.com/share/68b6b28e-4388-800f-87d2-34dfb34b8d36
