Adds a discover-logging/ build step that fetches the plasma-discover
source, instruments PKTransaction.cpp with qWarning calls at key points
(trigger, statusChanged, progressChanged, cleanup, errorFound,
installFile) to diagnose hanging .deb installs, then rebuilds and
reinstalls the patched packagekit-backend.so.
Also installs Firefox via the Mozilla apt repo (Ubuntu 24.04 ships
Firefox as a snap which doesn't work in the container).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
