Add an English translation of the corralito training-courses page

It was deliberately left Italian-only when /en support was first added;
now translated and following the same thin-page + shared-view pattern
as every other route, with the nav link and language switch no longer
special-casing it.

frontend/app/middleware/lang-switch.global.ts

@@ -38,10 +38,5 @@ export default defineNuxtRouteMiddleware(async (to) => {
     return
   }
 
-  if (bare === '/come-difendersi-dal-corralito') {
-    langSwitch.value = { available: false, fallback: '/en' }
-    return
-  }
-
   langSwitch.value = { available: true, fallback: '/en' }
 })