feat(authentication): update demo code hint for consistency

This change updates the demo verification code hint on the email code verification page to use a hardcoded string. This makes its implementation consistent with the recently added demo email hint, ensuring both are displayed in the same manner during demonstrations.

Author: fulleni

lib/authentication/view/email_code_verification_page.dart

@@ -82,7 +82,7 @@ class EmailCodeVerificationPage extends StatelessWidget {
                               children: [
                                 const SizedBox(height: AppSpacing.md),
                                 Text(
-                                  l10n.demoVerificationCodeMessage('123456'),
+                                  'For demo, use code: 123456',
                                   style: textTheme.bodyMedium?.copyWith(
                                     color: colorScheme.secondary,
                                     fontWeight: FontWeight.bold,