Update the tw uuid in backlog after task backup restoration.

Read the tw uuid/code from the backlog.data first line before importing backup, and modify it in the first line of the backup restoration after importing the backup, so that the taskwarrior is able to sync after backup importation.

Start by locating the backup restoration flow in the installer and inspect how the first line of backlog.data is handled before and after importing a backup. Verify the restored Taskwarrior data uses the original tw uuid and that Taskwarrior can sync after restoration.

Written by the indexing model from the issue text.