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/test-zone-data/DNSSEC-TP/dnssec10/README-DNSSEC-utilities.md

@@ -0,0 +1,9 @@
+# DNSEC utilities
+
+For these test scenarios there are three useful utilities avaiable:
+
+* keytag-from-dnskey
+* sign-rrset
+* verify-rrset
+
+See the [utilities directory README](../../utils/README.md) for details.