feat(frontend): refine app shell and assistant editors

frontend/src/components/layout/Topbar.tsx

@@ -1,41 +1,13 @@
-import { Bell, HelpCircle } from "lucide-react";
-import { Button } from "@/components/ui/button";
-import { ThemeToggle } from "./ThemeToggle";
-import {
-  Tooltip,
-  TooltipContent,
-  TooltipProvider,
-  TooltipTrigger,
-} from "@/components/ui/tooltip";
+import type { Ref } from "react";
 
-export function Topbar() {
+export function Topbar({
+  contentRef,
+}: {
+  contentRef: Ref<HTMLDivElement>;
+}) {
   return (
-    <header className="flex h-16 shrink-0 items-center justify-end gap-2 border-b border-border bg-background px-8">
-      <TooltipProvider>
-        <Button
-          variant="outline"
-          size="lg"
-          className="border-hairline-strong text-muted-foreground hover:bg-surface-strong hover:text-foreground"
-        >
-          <HelpCircle />
-          帮助
-        </Button>
-
-        <ThemeToggle />
-
-        <Tooltip>
-          <TooltipTrigger asChild>
-            <Button
-              variant="outline"
-              size="icon-lg"
-              className="border-hairline-strong text-muted-foreground hover:bg-surface-strong hover:text-foreground"
-            >
-              <Bell />
-            </Button>
-          </TooltipTrigger>
-          <TooltipContent side="bottom">通知</TooltipContent>
-        </Tooltip>
-      </TooltipProvider>
+    <header className="flex h-16 shrink-0 items-center border-b border-border bg-background px-4 sm:px-6 lg:px-8">
+      <div ref={contentRef} className="flex h-full min-w-0 flex-1 items-center" />
     </header>
   );
 }