The map canvas now fills its panel and draws through a view transform,
so it stays sharp at every zoom level. The wheel zooms around the
pointer, dragging with the middle button pans, and right click clears
the selection. The wheel listener is attached natively and non-passive
because Leptos delegates `wheel` to the document, where browsers ignore
`preventDefault`.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Steve Biedermann