Dependency arrows hold cards consistently in the queue

An arrow drawn from one card to another holds the second card until the first has finished. The queue now treats such an arrow as a wait everywhere: two cards can no longer end up waiting for each other, a card started anyway stays started even when it first has to wait for a free workspace, and removing an arrow leaves exactly the waits Obeya found on its own. An arrow drawn onto a card that is waiting for a workspace holds it too.