feat: add frontend auth shell

frontend/src/components/app/AppTopbar.tsx

@@ -1,10 +1,13 @@
-import { Bell, ChevronRight, UserRound } from 'lucide-react'
+import { Bell, ChevronRight, LogOut, UserRound } from 'lucide-react'
 
 import { Badge } from '@/components/ui/badge'
 import { Button } from '@/components/ui/button'
 import { Separator } from '@/components/ui/separator'
+import { useAuth } from '@/features/auth/AuthProvider'
 
 export function AppTopbar() {
+  const { logout, user } = useAuth()
+
   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">
@@ -20,7 +23,11 @@ export function AppTopbar() {
         </Button>
         <Button variant="ghost" className="gap-2">
           <UserRound className="size-4" />
-          <span>系统管理员</span>
+          <span>{user?.display_name || user?.username || '当前用户'}</span>
+        </Button>
+        <Button variant="outline" className="gap-2" onClick={() => void logout()}>
+          <LogOut className="size-4" />
+          <span>退出</span>
         </Button>
       </div>
     </header>