Add locale switcher component and integrate internationalization improvements

- Introduced `LocaleSwitcher` component for language selection with support for locale-aware dropdown and ARIA accessibility.
- Updated layouts (`Header`, `Breadcrumbs`, `Home`) to include the new locale switcher.
- Expanded localization files (`en.json`, `it.json`) with new keys for language switching.
- Adjusted i18n configuration to enhance routing and message imports.
- Updated Jest module mappings to mock new i18n components and utilities.

frontend/messages/en.json

@@ -161,5 +161,11 @@
     "maxLength": "Maximum {count} characters allowed",
     "pattern": "Invalid format",
     "passwordMismatch": "Passwords do not match"
+  },
+  "locale": {
+    "en": "English",
+    "it": "Italian",
+    "switchLanguage": "Switch language",
+    "currentLanguage": "Current language"
   }
 }

frontend/messages/it.json

@@ -161,5 +161,11 @@
     "maxLength": "Massimo {count} caratteri consentiti",
     "pattern": "Formato non valido",
     "passwordMismatch": "Le password non corrispondono"
+  },
+  "locale": {
+    "en": "Inglese",
+    "it": "Italiano",
+    "switchLanguage": "Cambia lingua",
+    "currentLanguage": "Lingua corrente"
   }
 }