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/home-dock.tsx

@@ -2,13 +2,15 @@
 
 import { Dock, DockIcon } from "@/components/ui/dock";
 import { signOut } from "next-auth/react";
-import { Home, User, LogOut, Download, BookOpen, LayoutDashboard } from "lucide-react";
+import { Home, User, LogOut, Download, BookOpen, LayoutDashboard, Bookmark } from "lucide-react";
 
 export function HomeDock({
   isAuthenticated,
+  isAdmin,
   onLoginClick,
 }: {
   isAuthenticated: boolean;
+  isAdmin: boolean;
   onLoginClick?: () => void;
 }) {
   return (
@@ -46,6 +48,13 @@ export function HomeDock({
             </a>
           </DockIcon>
         )}
+        {isAdmin && (
+          <DockIcon>
+            <a href="/bookmarks" aria-label="书签">
+              <Bookmark className="h-5 w-5 text-slate-700" />
+            </a>
+          </DockIcon>
+        )}
         <DockIcon>
           {isAuthenticated ? (
             <button