Guesthouse VMs

Community images with compressed disks now import. The community ARM64 Omarchy build ships a compressed qcow2, and the import used to stop on it with an error telling you to convert the disk yourself. Guesthouse now expands those disks while it converts, so the image it downloads installs on its own. The window stays live while a disk is imported. Unpacking an archive, converting a qcow2, and copying a prebuilt disk all ran on the main thread and left the app unresponsive for minutes. They now run off it, so the machine list, the progress, and Cancel keep working. Installation progress says which step is running. Downloading, verifying, unpacking, converting, and preparing each label their own progress bar, instead of several unlabelled passes from 0 to 100%.