The map's maxZoom bump from 10 to 16 in 3.1.2 expanded markercluster's
internal cluster tree by six zoom levels, exposing a markercluster bug
where a cluster's _bounds could end up undefined and crash _zoomEnd
("Cannot read properties of undefined (reading 'lat')"). The crash
left the marker pane completely empty and clusters unclickable.

Setting disableClusteringAtZoom: 11 on the cluster group caps the
cluster tree depth — beyond zoom 11 markers display individually
anyway, so there's no behavioural cost.

Closes #110.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>