feat: MVP-5 Sprint 1 - Backup/Restore system

- Add backup types and RecallBackup format
- Create backup snapshot engine (createBackupSnapshot)
- Add IndexedDB storage for local backups
- Implement retention policy (max 10, 30-day cleanup)
- Add backup validation and restore logic (merge/replace modes)
- Add backup restore UI dialog with preview and confirmation
- Add unsaved changes guard hook
- Integrate backups section in Settings
- Add backup endpoint to export-import API

src/app/settings/page.tsx

@@ -1,10 +1,11 @@
 'use client'
 
 import { useState, useRef } from 'react'
-import { Download, Upload } from 'lucide-react'
+import { Download, Upload, History } from 'lucide-react'
 import { Button } from '@/components/ui/button'
 import { Card, CardContent, CardDescription, CardHeader, CardTitle } from '@/components/ui/card'
 import { toast } from 'sonner'
+import { BackupList } from '@/components/backup-list'
 
 function parseMarkdownToNote(content: string, filename: string) {
   const lines = content.split('\n')
@@ -144,6 +145,21 @@ export default function SettingsPage() {
             </Button>
           </CardContent>
         </Card>
+
+        <Card>
+          <CardHeader>
+            <CardTitle className="flex items-center gap-2">
+              <History className="h-5 w-5" />
+              Backups
+            </CardTitle>
+            <CardDescription>
+              Restaura notas desde backups guardados localmente en tu navegador.
+            </CardDescription>
+          </CardHeader>
+          <CardContent>
+            <BackupList />
+          </CardContent>
+        </Card>
       </div>
     </main>
   )