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/(main)/dashboard/bookmarks/page.tsx

@@ -0,0 +1,16 @@
+import type { Metadata } from "next";
+import { redirect } from "next/navigation";
+import { auth } from "@/auth";
+import { BookmarkManager } from "./bookmark-manager";
+
+export const metadata: Metadata = {
+  title: "书签管理",
+};
+
+export default async function BookmarksPage() {
+  const session = await auth();
+  const role = (session?.user as { role?: string } | undefined)?.role;
+  if (role !== "admin") redirect("/unauthorized");
+
+  return <BookmarkManager />;
+}