Card search on the slash key

The slash key opens a search over the canvas's cards. Until it has been used once, a canvas with more than five cards shows a "Type / to search" button that explains the key and then goes away. Before the first word, the search lists the canvas's cards, the most recently changed first, and a card whose agent writes a line moves to the top at once. The row under the pointer lights up its card on the canvas; a card half or more behind the list, or out of sight, is pointed to by an indicator. Typed words find cards on the canvas and in the archive, and Enter opens the picked one.