feat: Заметки редактора в admin zeropost.ru

- app/admin/(protected)/notes/page.js: управление заметками
- app/admin/api/notes/route.js: GET+POST прокси к engine
- app/admin/api/notes/[id]/route.js: PATCH+DELETE
- lib/engine.js: createNote, updateNote, deleteNote
- components/admin/AdminNav.js: пункт «Заметки» с иконкой

components/admin/AdminNav.js

@@ -1,13 +1,14 @@
 'use client';
 import Link from 'next/link';
 import { usePathname, useRouter } from 'next/navigation';
-import { LayoutDashboard, FileText, Radio, Zap, Settings, LogOut, ExternalLink } from 'lucide-react';
+import { LayoutDashboard, FileText, Radio, Zap, Settings, LogOut, ExternalLink, MessageCircle } from 'lucide-react';
 
 const NAV = [
   { href: '/admin', label: 'Дашборд', icon: LayoutDashboard, exact: true },
   { href: '/admin/articles', label: 'Статьи', icon: FileText },
   { href: '/admin/channels', label: 'Каналы', icon: Radio },
   { href: '/admin/autogen', label: 'Автогенерация', icon: Zap },
+  { href: '/admin/notes', label: 'Заметки', icon: MessageCircle },
   { href: '/admin/settings', label: 'Настройки', icon: Settings },
 ];