Stacked avatar group with an overflow pill. Project <cngx-avatar> children;
with [max] set, the group shows the first max and renders a +N pill for
the rest. The visible/hidden split is a computed() over the projected
avatars and max - the overflow count is derived, never tracked by hand
(Pillar 1) - and the group carries an aria-label summarising the total and
hidden counts so assistive tech hears "7 teammates, 4 not shown".