test(clients): follow the windows client from island to tray flyout

Three tests still described the top-edge island the flyout rewrite replaced, and had
been failing since it landed. The silhouette test is gone with its subject: IslandShape
was a custom-painted capsule, and a flyout is a Border. The click-through test keeps its
requirement -- nothing of ours over anybody's window while idle -- but the flyout meets
it by being hidden rather than by handing its input back, so it now asserts that. The
context-menu guard only changed shape.