frontend: rebuild bookmark page with drag-and-drop, search, and theme system

- bookmark management with dnd-kit reordering, bulk edit, search,
  category filter/rename, and meta auto-fetch
- migrate /bookmarks → /dashboard/bookmarks under (main) layout
- homepage redesign with category grid, /-key search, dock tooltips
- theme toggle + use-theme, sonner toasts, alert-dialog/skeleton,
  visual refresh of auth pages

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/app/page.tsx

@@ -30,32 +30,16 @@ async function fetchPublicBookmarks(): Promise<Bookmark[]> {
 export default async function HomePage() {
   const session = await auth();
   const isAuthenticated = !!session?.user;
-  const isAdmin = (session?.user as any)?.role === "admin";
+  const role = (session?.user as { role?: string } | undefined)?.role;
+  const isAdmin = role === "admin";
 
-  let healthText = "无法连接到后端服务";
-  let bookmarks: Bookmark[] = [];
-
-  try {
-    const res = await fetch(`${SERVER_API_URL}/api/health`, {
-      cache: "no-store",
-    });
-    if (res.ok) {
-      healthText = await res.text();
-    } else {
-      healthText = `后端异常: ${res.status}`;
-    }
-  } catch {
-    healthText = "后端连接失败";
-  }
-
-  bookmarks = await fetchPublicBookmarks();
+  const bookmarks = await fetchPublicBookmarks();
 
   return (
     <Suspense>
       <HomePageClient
         isAuthenticated={isAuthenticated}
         isAdmin={isAdmin}
-        healthText={healthText}
         hasKeycloak={hasKeycloak}
         bookmarks={bookmarks}
       />