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/SPF.pm

@@ -0,0 +1,38 @@
+package Zonemaster::LDNS::RR::SPF;
+
+use strict;
+use warnings;
+
+use parent 'Zonemaster::LDNS::RR';
+
+sub spfdata() {
+    my ($rr) = @_;
+
+    return join( "", map { substr($rr->rdf($_ - 1), 1) } 1..$rr->rd_count() );
+}
+
+1;
+
+=head1 NAME
+
+Zonemaster::LDNS::RR::SPF - Type SPF 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 spfdata()
+
+Returns the concatenation of all the strings composing the data of the resource record.
+
+For example, if an SPF resource record has the following presentation format:
+
+    test.example. 3600 IN SPF "v=spf1 " "mx " "a " "-all"
+
+then C<spfdata()> returns the string C<"v=spf1 mx a -all">.
+
+=back