The index produced by drag-and-drop refers to the rendered task list,
which excludes completed tasks when hideCompletedTasks is enabled, but
selectNextTaskPosition resolved that index against the unfiltered task
array, computing positions between the wrong (often hidden) neighbors.
Lift the completed-tasks visibility state up to TaskLists so the drag
end handler can pass it through the move action, and apply the same
filter in selectNextTaskPosition that the rendered list uses.
Fixes#1718
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
