style(webui): clarify surface hierarchy (#5029)

webui/src/components/Sidebar.tsx

@@ -14,7 +14,6 @@ import { useTranslation } from "react-i18next";
 import { ChatList } from "@/components/ChatList";
 import { ConnectionBadge } from "@/components/ConnectionBadge";
 import { Button } from "@/components/ui/button";
-import { Separator } from "@/components/ui/separator";
 import type {
   ChatSummary,
   SidebarViewState,
@@ -90,7 +89,6 @@ export function Sidebar(props: SidebarProps) {
       className={cn(
         "flex h-full w-full min-w-0 flex-col text-sidebar-foreground",
         props.hostChromeInset ? "bg-transparent" : "bg-sidebar",
-        !props.hostChromeInset && "border-r border-sidebar-border/60",
       )}
     >
       <div
@@ -223,10 +221,9 @@ export function Sidebar(props: SidebarProps) {
           />
         )}
       </div>
-      <Separator className="bg-sidebar-border/50" />
       <div
         className={cn(
-          "flex items-center gap-1 px-2.5 py-2.5 text-xs",
+          "flex items-center gap-1 bg-sidebar/55 px-2.5 py-3 text-xs",
           collapsed && "w-14 flex-col px-0",
         )}
       >