[fakayser]

Deleting a folder could remove its files and empty descendants while leaving the now-empty folder itself on disk. The cleanup loop used the directory list captured before its children were removed.

Recheck the current directory contents during bottom-up cleanup. This removes newly empty parents while preserving remaining files and neighbouring directories. The same behavior applies at every folder depth.

Validation: 29 focused backend tests passed, including nested empty-directory cleanup and preservation of non-empty directories; Ruff checks/format and documentation checks passed. Two frontend-to-real-backend browser scenarios passed, including deleting a root with unregistered empty descendants and deleting a zone root without changing Zones.