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/example.spec.ts

@@ -0,0 +1,18 @@
+import { test, expect } from '@playwright/test';
+
+test('has title', async ({ page }) => {
+  await page.goto('https://playwright.dev/');
+
+  // Expect a title "to contain" a substring.
+  await expect(page).toHaveTitle(/Playwright/);
+});
+
+test('get started link', async ({ page }) => {
+  await page.goto('https://playwright.dev/');
+
+  // Click the get started link.
+  await page.getByRole('link', { name: 'Get started' }).click();
+
+  // Expects page to have a heading with the name of Installation.
+  await expect(page.getByRole('heading', { name: 'Installation' })).toBeVisible();
+});