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/t/serialize.t

@@ -0,0 +1,18 @@
+use Test::More;
+use JSON::PP;
+
+use_ok( 'Zonemaster::LDNS' );
+
+my $p = Zonemaster::LDNS::Packet->new( 'www.iis.se', 'A', 'IN' );
+$p->answerfrom( '127.0.0.1' );
+$p->timestamp( '1384423749.28615' );
+
+my $json = JSON::PP->new->allow_blessed->convert_blessed;
+my $ref  = decode_json $json->encode( $p );
+is( $ref->{'Zonemaster::LDNS::Packet'}{answerfrom}, '127.0.0.1' );
+
+my $decode = JSON::PP->new->filter_json_single_key_object(
+    'Zonemaster::LDNS::Packet' => sub { is $_[0]->{answerfrom}, '127.0.0.1'; return; } );
+$decode->decode( $json->encode( $p ) );
+
+done_testing;