One placeholder row in the first-load body, replacing the built-in
marker-rail-and-two-bars shape. Rendered [skeletonRowCount] times.
Contextless, and deliberately so: a placeholder stands in for a row whose
data has not arrived, so there is nothing to hand it. Bind this when the
real rows are taller or busier than the default shape and the swap to
content would otherwise reflow the page.
Whatever renders here sits inside an aria-hidden wrapper - the load is
announced through the timeline's live region, not through the placeholder.