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/NSEC.pm

@@ -0,0 +1,47 @@
+package Zonemaster::LDNS::RR::NSEC;
+
+use strict;
+use warnings;
+
+use parent 'Zonemaster::LDNS::RR';
+
+sub nxtdname {
+    return $_[0]->next;
+}
+
+1;
+
+=head1 NAME
+
+Zonemaster::LDNS::RR::NSEC - Type NSEC record
+
+=head1 DESCRIPTION
+
+A subclass of L<Zonemaster::LDNS::RR>, so it has all the methods of that class available in addition to the ones documented here.
+
+=head1 METHODS
+
+=over
+
+=item next()
+
+Returns the next name.
+
+=item nxtdname()
+
+Alias for C<next()>.
+
+=item typelist()
+
+Returns a string with the typelist. The string has the type names separated by spaces.
+
+=item typehref()
+
+Returns a reference to a hash, where the keys are the type names and the corresponding values are true. That is, if you look for a type in this hash
+you get a true value back if the record covers it and false if not.
+
+=item covers($name)
+
+Returns true or false depending on if the record covers the given name or not.
+
+=back