feat: add enterprise app ui layer

frontend/src/components/app/AppTopbar.tsx

@@ -0,0 +1,28 @@
+import { Bell, ChevronRight, UserRound } from 'lucide-react'
+
+import { Badge } from '@/components/ui/badge'
+import { Button } from '@/components/ui/button'
+import { Separator } from '@/components/ui/separator'
+
+export function AppTopbar() {
+  return (
+    <header className="sticky top-0 z-20 flex h-14 items-center justify-between border-b border-border bg-surface/95 px-6 backdrop-blur">
+      <div className="flex min-w-0 items-center gap-2 text-sm">
+        <span className="font-medium text-foreground">AI 工单平台</span>
+        <ChevronRight className="size-4 text-muted-foreground" />
+        <span className="truncate text-muted-foreground">当前工作区</span>
+      </div>
+      <div className="flex items-center gap-3">
+        <Badge variant="info">本地环境</Badge>
+        <Separator orientation="vertical" className="h-5" />
+        <Button variant="ghost" size="icon" aria-label="通知">
+          <Bell className="size-4" />
+        </Button>
+        <Button variant="ghost" className="gap-2">
+          <UserRound className="size-4" />
+          <span>系统管理员</span>
+        </Button>
+      </div>
+    </header>
+  )
+}