PaneHeader

PaneHeader anatomy — Identity (Avatar + Text with ellipsized Name / muted Sub) and Actions (ml-auto flex row) with Actions.Sep hairlines; the Sep hides while the InlineSearch is expanded.

ContentAreaHeader — same slots via props (avatar/title/subtitle/actions, or titleNode/subtitleNode for custom chrome). Wrapper here carries `data-content-panel`, so the header self-paints the dark content layer; inside an already-dark Pane it stays transparent.