Function paint_panel_header 

pub fn paint_panel_header(
    ui: &mut dyn UiBuilder,
    panel_rect: [f32; 4],
    height: f32,
    theme: &UiTheme,
)

Paints a panel-header strip: subtle gradient bg, hairline at bottom, then a row of tabs returned through tabs_clicked and a row of action icons on the right. Returns the y-coordinate where panel content can begin.