A new Skeleton (a shimmering shape, still where motion is off) and a region
that tells assistive tech once that something is loading. The agent card's
header is split into AgentCardLayout, a layout with a slot for each part: the
card fills the slots with the real icon, badges and controls, its new
AgentCardSkeleton twin fills the same slots with placeholder shapes, so the
card that replaces it lands in the same place. The agents page uses the twin in
place of its "loading…" text.