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/utils/README.md

@@ -0,0 +1,18 @@
+# Utilities for test zones
+
+## keytag-from-dnskey
+
+The [keytag-from-dnskey](keytag-from-dnskey) utility provides the key tag for a
+DNSKEY record. Run `keytag-from-dnskey --help` for manual.
+
+## sign-rrset
+
+The [sign-rrset](sign-rrset) utility creates a valid RRSIG for an RRset using
+the private key provided. Run `sign-rrset --help` for manual.
+
+## verify-rrset
+
+The [verify-rrset](verify-rrset) utility verifies if the provided RRSIG is a
+valid signature for the given RRset using the provided DNSKEY. Run
+`verify-rrset --help` for manual.
+