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/jest.config.js

@@ -10,8 +10,10 @@ const customJestConfig = {
   setupFilesAfterEnv: ['<rootDir>/jest.setup.js'],
   testEnvironment: 'jest-environment-jsdom',
   moduleNameMapper: {
+    '^next-intl$': '<rootDir>/tests/__mocks__/next-intl.tsx',
     '^next-intl/routing$': '<rootDir>/tests/__mocks__/next-intl-routing.tsx',
     '^next-intl/navigation$': '<rootDir>/tests/__mocks__/next-intl-navigation.tsx',
+    '^@/components/i18n$': '<rootDir>/tests/__mocks__/components-i18n.tsx',
     '^@/(.*)$': '<rootDir>/src/$1',
   },
   testMatch: ['<rootDir>/tests/**/*.test.ts', '<rootDir>/tests/**/*.test.tsx'],