Finished cards give their workspace back

A card stopped with work on its branch used to keep its clone, so it could go on there later. When its work was then merged by hand and the plan doc ticked it off, the card showed as done but its clone stayed taken for good, and neither a button nor a restart freed it. Deleted cards did the same. Now Obeya gives such workspaces back as soon as the plan doc ticks the workstream off or the card is deleted, and frees any left over the next time it starts. The branch stays in the clone, and undoing a delete brings the card back with its clone.