Remove i18n, keep only Italian and rely on browser translation

The interface was translated in en/it/es/fr via @nuxtjs/i18n. Drop the
module, the locale files, and the language switcher: the UI is now
static Italian text, with translation for foreign visitors left to the
Google Translate browser extension instead of the app.

frontend/shared/utils/format.ts

@@ -1,13 +1,13 @@
 /** Human-readable date for display; returns an empty string when unset. */
-export function formatDate(value: string | null | undefined, locale = 'en-GB'): string {
+export function formatDate(value: string | null | undefined): string {
   if (!value) return ''
-  return new Intl.DateTimeFormat(locale, { dateStyle: 'long' }).format(new Date(value))
+  return new Intl.DateTimeFormat('it-IT', { dateStyle: 'long' }).format(new Date(value))
 }
 
 /** Date and time of publication, shown in the article byline. */
-export function formatDateTime(value: string | null | undefined, locale = 'en-GB'): string {
+export function formatDateTime(value: string | null | undefined): string {
   if (!value) return ''
-  return new Intl.DateTimeFormat(locale, { dateStyle: 'long', timeStyle: 'short' })
+  return new Intl.DateTimeFormat('it-IT', { dateStyle: 'long', timeStyle: 'short' })
     .format(new Date(value))
 }