SpoolBuddy devices can now be updated from Settings → Updates without
SSH access. The daemon picks up an "update" command via its existing
heartbeat, runs git fetch/reset + pip install, reports progress back
to the backend, then exits for systemd to restart with the new code.
Backend: update_status/update_message fields, trigger + status endpoints
Daemon: _perform_update() handler, report_update_status() API method
Frontend: "Apply Update" button with live progress in UpdatesTab