fix: change default language from Spanish to English

- Update default lng from 'es' to 'en'
- Update fallbackLng from 'es' to 'en'
- Application will now display in English by default
- Users can still switch to Spanish via language selector

https://claude.ai/code/session_01GNbnkFoESkRcnPr3bLCYDg

frontend/i18n.ts

@@ -11,8 +11,8 @@ i18n
       es: { translation: es },
       en: { translation: en },
     },
-    lng: localStorage.getItem('language') || 'es', // Español por defecto
-    fallbackLng: 'es', // Si falla una traducción, usa español
+    lng: localStorage.getItem('language') || 'en', // English by default
+    fallbackLng: 'en', // If translation fails, use English
     interpolation: {
       escapeValue: false, // React ya escapa por defecto
     },