Critical fix (found in production testing): restoring a backup containing a volume always…

v0.19.4-beta

Critical fix (found in production testing): restoring a backup containing a volume always failed on a self-hosted agent, and always had. The archive was extracted into the system's default temporary folder (os.MkdirTemp("", ...)), invisible to the host's Docker daemon when the agent runs in its own container (only BackupsDir is mounted to the host) — the following docker run -v then mounted an empty folder, failing with tar: can't open '/src/volume-*.tar.gz': No such file or directory. Extraction now happens under BackupsDir, consistent with the backup side.