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/t/manifest.t

@@ -0,0 +1,37 @@
+#!perl
+use v5.14.2;
+use strict;
+use warnings;
+use utf8;
+use Test::More tests => 2;
+use Test::NoWarnings;
+
+use File::Basename qw( dirname );
+
+chdir dirname( dirname( __FILE__ ) ) or BAIL_OUT( "chdir: $!" );
+
+my $makebin = 'make';
+
+sub make {
+    my @make_args = @_;
+
+    undef $ENV{MAKEFLAGS};
+
+    my $command = join( ' ', $makebin, '-s', @make_args );
+    my $output = `$command 2>&1`;
+
+    if ( $? == -1 ) {
+        BAIL_OUT( "failed to execute: $!" );
+    }
+    elsif ( $? & 127 ) {
+        BAIL_OUT( "child died with signal %d, %s coredump\n", ( $? & 127 ), ( $? & 128 ) ? 'with' : 'without' );
+    }
+
+    return $output, $? >> 8;
+}
+
+subtest "distcheck" => sub {
+    my ( $output, $status ) = make "distcheck";
+    is $status, 0,  $makebin . ' distcheck exits with value 0';
+    is $output, "", $makebin . ' distcheck gives empty output';
+};