Header now spans the full window width above the [sidebar | chat | right-sidebar] row instead of nesting inside the central column. The chat area becomes a self-contained framed window with its own border and rounded corners on all four sides, and sidebars sit flush against the header sharing its bg-sidebar so the seam is invisible.
Removed the duplicated shell controls the old layout needed to fake header-height inside sidebars: portal host on RightSidebar, paddingTop reservation, top drag overlay, duplicated layout-left / chat-new buttons in SidebarHeader, the showDesktopSidebarChrome block in SessionSidebar, and the conditional traffic-lights inset on the desktop header. Mac WCO inset now lives only on the header.
Moved the new-session action into the SessionSwitcher dropdown as its first item, removed the standalone chat-new button from the header, relocated scheduled-tasks into the left action group of the sidebar header, and bumped ContextPanel tab strip to h-10 to balance the more prominent header.
Bohdan Triapitsyn
471ae69b1a