The wheel did nothing over a preview picture, the text of a Callout or the
padding of a card, and the middle button did not pan there. Those parts of a
panel let the mouse through, so in the classic renderer the pointer lands on
the frontend's .dom-widget wrapper, which takes the mouse and hands nothing
on. The pack looked for its panel between the pointer and the wrapper and
found none. A pointer on the wrapper now counts as over the panel inside it.
scripts/dev/wheel_sweep.mjs turns the wheel at every point of every node and
reports each spot where the graph does not zoom. In the classic renderer 33
of the 41 nodes had such spots; none has one now. Nodes 2.0 had none.
