Refactor i18n integration and update tests for improved localization

- Updated test components (`PasswordResetConfirmForm`, `PasswordChangeForm`) to use i18n keys directly, ensuring accurate validation messages.
- Refined translations in `it.json` to standardize format and content.
- Replaced text-based labels with localized strings in `PasswordResetRequestForm` and `RegisterForm`.
- Introduced `generateLocalizedMetadata` utility and updated layout metadata generation for locale-aware SEO.
- Enhanced e2e tests with locale-prefixed routes and updated assertions for consistency.
- Added comprehensive i18n documentation (`I18N.md`) for usage, architecture, and testing.

frontend/src/app/[locale]/layout.tsx

@@ -4,6 +4,7 @@ import { notFound } from 'next/navigation';
 import { routing } from '@/lib/i18n/routing';
 import { NextIntlClientProvider } from 'next-intl';
 import { getMessages } from 'next-intl/server';
+import { generateLocalizedMetadata, type Locale } from '@/lib/i18n/metadata';
 import '../globals.css';
 import { Providers } from '../providers';
 import { AuthProvider } from '@/lib/auth/AuthContext';
@@ -23,10 +24,14 @@ const geistMono = Geist_Mono({
   preload: false, // Only preload primary font
 });
 
-export const metadata: Metadata = {
-  title: 'FastNext Template',
-  description: 'FastAPI + Next.js Template',
-};
+export async function generateMetadata({
+  params,
+}: {
+  params: Promise<{ locale: string }>;
+}): Promise<Metadata> {
+  const { locale } = await params;
+  return generateLocalizedMetadata(locale as Locale);
+}
 
 export default async function LocaleLayout({
   children,