frontend: add bookmark management and homepage navigation

Admin-only /bookmarks page for managing entries; homepage now renders
public bookmarks as a category-grouped navigation grid (empty state
links admin to the manager). Dashboard gains a recent-bookmarks card,
dock and main layout get a bookmark entry for admins, and the
middleware protects /bookmarks.

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

frontend/app/bookmarks/page.tsx

@@ -0,0 +1,22 @@
+import { auth } from "@/auth";
+import { redirect } from "next/navigation";
+import { BookmarkManager } from "./bookmark-manager";
+
+export default async function BookmarksPage() {
+  const session = await auth();
+  if (!session?.user) {
+    redirect("/login");
+  }
+
+  const role = (session.user as any)?.role;
+  if (role !== "admin") {
+    redirect("/unauthorized");
+  }
+
+  return (
+    <div>
+      <h1 className="mb-6 text-2xl font-bold">书签管理</h1>
+      <BookmarkManager />
+    </div>
+  );
+}