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/sitemap.ts

@@ -0,0 +1,49 @@
+import { MetadataRoute } from 'next';
+import { routing } from '@/lib/i18n/routing';
+
+/**
+ * Generate multilingual sitemap
+ * Includes all public routes for each supported locale
+ */
+export default function sitemap(): MetadataRoute.Sitemap {
+  const baseUrl = process.env.NEXT_PUBLIC_SITE_URL || 'http://localhost:3000';
+
+  // Define public routes that should be in sitemap
+  const publicRoutes = [
+    '', // homepage
+    '/login',
+    '/register',
+    '/password-reset',
+    '/demos',
+    '/dev',
+    '/dev/components',
+    '/dev/layouts',
+    '/dev/forms',
+    '/dev/docs',
+  ];
+
+  // Generate sitemap entries for each locale
+  const sitemapEntries: MetadataRoute.Sitemap = [];
+
+  routing.locales.forEach((locale) => {
+    publicRoutes.forEach((route) => {
+      const path = route === '' ? `/${locale}` : `/${locale}${route}`;
+
+      sitemapEntries.push({
+        url: `${baseUrl}${path}`,
+        lastModified: new Date(),
+        changeFrequency: route === '' ? 'daily' : 'weekly',
+        priority: route === '' ? 1.0 : 0.8,
+        // Language alternates for this URL
+        alternates: {
+          languages: {
+            en: `${baseUrl}/en${route}`,
+            it: `${baseUrl}/it${route}`,
+          },
+        },
+      });
+    });
+  });
+
+  return sitemapEntries;
+}