Install/Backup button sends a cancel while a download or upload is running

[eliasbakken]

Found by reading the code while testing v1.1.0-RC8-2-g23a2bb6. Not reproduced on a board.

Install/Backup button fires a cancel during a download or upload

In App.vue:

• isInstallButtonDisabled() returns false whenever state != "IDLE" ("this button means Cancel").
• installButtonText() only says Cancel for INSTALLING/BACKUPING.
• onInstallButtonClick() calls cancel_installation (or cancel_backup) for any non-IDLE state.

During DOWNLOADING/UPLOADING, with an image already selected (seen live: Install stayed enabled while an upload ran), the button reads Install, is enabled, and clicking it sends cancel_installation = pkill -f xz -9. With nothing to kill, that returns exit 1 and shows an error toast. In backup mode it calls cancel_backup, which sets state CANCELLED and deletes images/<state.Filename>, where state.Filename is the file currently being downloaded or uploaded.

pkill -f xz -9

Used by both cancelInstallation and cancelBackup, it matches any process whose command line contains "xz", including anything handling a *.img.xz filename.

Suggest: disable the button unless state is IDLE or the matching operation, and cancel by PID or process group, not by pattern.

[eliasbakken]

Fixed in #158 (merged as d611c55), commits 6d0329d and 7553fcf. Jobs now run in their own process group and a cancel reaches only that group's xz, instead of pkill -f xz -9 matching anything with xz in its command line. The Install/Backup button is disabled outside IDLE and its own operation, and only sends a cancel for that operation; a cancel with nothing running is a no-op rather than an error toast.

Covered by a test that starts an unrelated xz pipeline and checks the cancel leaves it alone.