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-backend/lib/Zonemaster/Backend.pm

@@ -0,0 +1,24 @@
+package Zonemaster::Backend;
+
+our $VERSION = '12.0.0';
+
+use strict;
+use warnings;
+use 5.14.2;
+
+=head1 NAME
+
+Zonemaster::Backend - A system for running Zonemaster tests asynchronously through an RPC-API
+
+=head1 AUTHOR
+
+Michal Toma <toma@nic.fr>
+
+=head1 LICENSE
+
+This is free software under a 2-clause BSD license. The full text of the license can
+be found in the F<LICENSE> file included with this distribution.
+
+=cut
+
+1;