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/tests/components/settings/ProfileSettingsForm.test.tsx

@@ -72,7 +72,7 @@ describe('ProfileSettingsForm', () => {
     it('renders form with all fields', () => {
       renderWithProvider(<ProfileSettingsForm />);
 
-      expect(screen.getByText('Profile Information')).toBeInTheDocument();
+      expect(screen.getByText('Profile Settings')).toBeInTheDocument();
       expect(screen.getByLabelText(/first name/i)).toBeInTheDocument();
       expect(screen.getByLabelText(/last name/i)).toBeInTheDocument();
       expect(screen.getByLabelText(/email/i)).toBeInTheDocument();
@@ -103,7 +103,7 @@ describe('ProfileSettingsForm', () => {
     it('shows email cannot be changed message', () => {
       renderWithProvider(<ProfileSettingsForm />);
 
-      expect(screen.getByText(/cannot be changed from this form/i)).toBeInTheDocument();
+      expect(screen.getByText(/cannot be changed.*contact support/i)).toBeInTheDocument();
     });
 
     it('marks first name as required', () => {