Fix screenshot dimensions in PWA manifest

- Update desktop screenshot to 1920x1080 (was 1280x720)
- Update mobile screenshot to 614x853 (was 375x667)
- Keep tablet screenshot at 768x1024 (correct)

nuxt4/nuxt.config.ts

@@ -57,7 +57,7 @@ export default defineNuxtConfig({
       screenshots: [
         {
           src: '/screenshots/desktop-1.png',
-          sizes: '1280x720',
+          sizes: '1920x1080',
           type: 'image/png',
           form_factor: 'wide',
           label: 'Pantalla principal en escritorio'
@@ -71,7 +71,7 @@ export default defineNuxtConfig({
         },
         {
           src: '/screenshots/mobile-1.png',
-          sizes: '375x667',
+          sizes: '614x853',
           type: 'image/png',
           form_factor: 'narrow',
           label: 'Pantalla principal en móvil'