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/robots.ts

@@ -0,0 +1,21 @@
+import { MetadataRoute } from 'next';
+
+/**
+ * Generate robots.txt
+ * Configures search engine crawler behavior
+ */
+export default function robots(): MetadataRoute.Robots {
+  const baseUrl = process.env.NEXT_PUBLIC_SITE_URL || 'http://localhost:3000';
+
+  return {
+    rules: [
+      {
+        userAgent: '*',
+        allow: '/',
+        // Disallow authenticated routes
+        disallow: ['/admin/', '/settings/'],
+      },
+    ],
+    sitemap: `${baseUrl}/sitemap.xml`,
+  };
+}