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-ldns/lib/Zonemaster/LDNS/RR/CDS.pm

@@ -0,0 +1,24 @@
+package Zonemaster::LDNS::RR::CDS;
+
+use strict;
+use warnings;
+
+use parent 'Zonemaster::LDNS::RR::DS';
+
+1;
+
+=head1 NAME
+
+Zonemaster::LDNS::RR::CDS - Type CDS record
+
+=head1 DESCRIPTION
+
+A subclass of L<Zonemaster::LDNS::RR::DS>, so it has all the methods of that class available in addition to the ones documented here.
+
+=head1 METHODS
+
+No other specific methods implemented.
+
+Note that the inherited parent methods L<Zonemaster::LDNS::RR::DS/verify($other)> will always return false, as LDNS currently only supports the DS and DNSKEY RR types for this method.
+
+=cut