Add Clases Grabadas section with audio player and announcement system

- Copy and merge audio files from Nextcloud (joined clase 1 and 2)
- Create ClasesGrabadas page with audio player and download option
- Add SistemaAnuncios component for user notifications
- Add announcement about new audio classes feature
- Add link to Clases Grabadas in Dashboard
- Audio files: 4 classes (clase1-4_completa.m4a) ~890MB total

frontend/src/pages/Dashboard.tsx

@@ -8,7 +8,8 @@ import { ProgressBar } from '../components/progress/ProgressBar';
 import { ScoreDisplay } from '../components/progress/ScoreDisplay';
 import { BadgesSection } from '../components/progress/Badges';
 import { Loader } from '../components/ui/Loader';
-import { BookOpen, User, LogOut, LayoutGrid, Award, Star, Target, CheckCircle, FileText } from 'lucide-react';
+import { BookOpen, User, LogOut, LayoutGrid, Award, Star, Target, CheckCircle, FileText, Headphones } from 'lucide-react';
+import { SistemaAnuncios } from '../components/announcements/SistemaAnuncios';
 
 const MODULOS_CONFIG = [
   { id: 'modulo1', numero: 1, titulo: 'Fundamentos de Economía', descripcion: 'Introducción a los conceptos básicos', totalEjercicios: 3 },
@@ -121,6 +122,9 @@ export function Dashboard() {
           <p className="text-gray-600">Continúa donde lo dejaste y desbloquea nuevos logros</p>
         </div>
 
+        {/* Sistema de Anuncios */}
+        <SistemaAnuncios />
+
         {/* Stats Cards */}
         <div className="grid grid-cols-1 md:grid-cols-3 gap-6 mb-8">
           <Card className="bg-gradient-to-br from-blue-500 to-blue-600 text-white border-none">
@@ -252,6 +256,12 @@ export function Dashboard() {
                   Material PDF
                 </Button>
               </Link>
+              <Link to="/clases">
+                <Button variant="outline" size="lg" className="bg-gradient-to-r from-purple-50 to-pink-50 border-purple-200 hover:border-purple-300">
+                  <Headphones className="w-5 h-5 mr-2 text-purple-600" />
+                  <span className="text-purple-700">Clases Grabadas</span>
+                </Button>
+              </Link>
             </div>
           </div>