feat: add full Zonemaster stack with Docker and Spanish UI

- Clone all 5 Zonemaster component repos (LDNS, Engine, CLI, Backend, GUI)
- Dockerfile.backend: 8-stage multi-stage build LDNS→Engine→CLI→Backend
- Dockerfile.gui: Astro static build served via nginx
- docker-compose.yml: backend (internal) + frontend (port 5353)
- nginx.conf: root redirects to /es/, /api/ proxied to backend
- zonemaster-gui/config.ts: defaultLanguage set to 'es' (Spanish)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

zonemaster-gui/e2e/FR05.e2e-spec.ts

@@ -0,0 +1,33 @@
+import { test, expect } from './global-setup';
+
+import { goToHome, setLang } from './utils/app.utils';
+
+test.describe('Zonemaster test FR05 - [Supports internationalization]', () => {
+  test.beforeEach(async ({ page }) => {
+    await goToHome(page);
+  });
+
+  const testSuite = [
+      { language: 'Danish', code: 'da', expected: 'Domænenavn' },
+      { language: 'English', code: 'en', expected: 'Domain name' },
+      { language: 'Spanish', code: 'es', expected: 'Nombre de dominio' },
+      { language: 'Finnish', code: 'fi', expected: 'Verkkotunnuksen nimi' },
+      { language: 'French', code: 'fr', expected: 'Nom de domaine' },
+      { language: 'Norwegian', code: 'nb', expected: 'Domenenavn' },
+      { language: 'Swedish', code: 'sv', expected: 'Domänamn' },
+      { language: 'Slovenian', code: 'sl', expected: 'Ime domene' },
+  ];
+
+  for (const { language, code, expected } of testSuite) {
+    test(`should have ${language} language option`, async ({ page }) => {
+      const langNavLink = page.locator(`select#languageSwitcher > option[lang="${code}"]`);
+      await expect(langNavLink).toHaveCount(1);
+      await expect(langNavLink).toHaveAttribute('lang', code);
+    })
+
+    test(`should switch to ${language}`, async ({ page }) => {
+      await setLang(page, code);
+        await expect(page.locator('input[name="domain"]')).toHaveAttribute('placeholder', expected);
+    })
+  }
+});