Workstream cards keep their workstream when the plan doc changes

A project's cards follow the checklist in its plan doc. Before, cards stayed at their place in the list, so when a doc dropped finished workstreams and added new ones, a new workstream could take over an old one's conversation and show as done. Now each card follows its workstream by its label or, without one, by its title, in any script, also when dropping a sibling changes how an item reads. A card that was worked on and whose workstream leaves the doc keeps its history as a task of its own; for a plan folder outside the repository, only once the workstream stayed away for five minutes.