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-engine/share/json2yaml.pl

@@ -0,0 +1,33 @@
+#!/usr/bin/env perl
+
+use 5.014002;
+use strict;
+use warnings;
+
+use File::ShareDir qw[dist_file];
+use File::Slurp;
+
+use Zonemaster::Engine::Profile;
+
+my $json_file = @ARGV ? $ARGV[0] : dist_file( 'Zonemaster-Engine', 'profile.json');
+my $json = read_file( $json_file );
+my $profile = Zonemaster::Engine::Profile->from_json( $json );
+my $yaml = $profile->to_yaml();
+say $yaml;
+
+=head1 NAME
+
+json2yaml - Convert a JSON profile into YAML
+
+=head1 SYNOPSIS
+
+    ./json2yaml.pl
+    ./json2yaml.pl profile.json
+
+=head1 DESCRIPTION
+
+json2yaml converts a JSON profile into YAML. The JSON profile can be passed as
+an argument. If no argument is provided, the script will look for the default
+profile. The YAML profile is written to the standard output.
+
+=cut