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/lib/Zonemaster/Engine/Normalization/Error.pm

@@ -0,0 +1,147 @@
+package Zonemaster::Engine::Normalization::Error;
+
+use v5.16.0;
+use warnings;
+
+use Carp;
+use Readonly;
+use Locale::TextDomain qw[Zonemaster-Engine];
+
+use overload '""' => \&string;
+
+
+=head1 NAME
+
+Zonemaster::Engine::Normalization::Error - normalization error class
+
+
+=head1 SYNOPSIS
+
+    use Zonemaster::Engine::Normalization::Error;
+
+    my $error = Zonemaster::Engine::Normalization::Error->new(LABEL_TOO_LONG => {label => $label});
+
+=cut
+
+
+Readonly my %ERRORS => (
+    AMBIGUOUS_DOWNCASING => {
+        message => N__ 'Ambiguous downcasing of character "{unicode_name}" in the domain name. Use all lower case instead.',
+        arguments => [ 'unicode_name' ]
+    },
+    DOMAIN_NAME_TOO_LONG => {
+        message => N__ 'Domain name is too long (more than 253 characters with no final dot).',
+    },
+    EMPTY_DOMAIN_NAME => {
+        message => N__ 'Domain name is empty.'
+    },
+    INITIAL_DOT => {
+        message => N__ 'Domain name starts with dot.'
+    },
+    INVALID_ASCII => {
+        message => N__ 'Domain name has an ASCII label ("{label}") with a character not permitted.',
+        arguments => [ 'label' ]
+    },
+    INVALID_U_LABEL => {
+        message => N__ 'Domain name has a non-ASCII label ("{label}") which is not a valid U-label.',
+        arguments => [ 'label' ]
+    },
+    REPEATED_DOTS => {
+        message => N__ 'Domain name has repeated dots.'
+    },
+    LABEL_TOO_LONG => {
+        message => N__ 'Domain name has a label that is too long (more than 63 characters), "{label}".',
+        arguments => [ 'label' ]
+    },
+);
+
+=head1 ATTRIBUTES
+
+=over
+
+=item tag
+
+The message tag associated to the error.
+
+=item params
+
+The error message parameters to use in the message string.
+
+=back
+
+=head1 METHODS
+
+=over
+
+=item new($tag, $params)
+
+Creates and returns a new error object.
+This function will croak if there is a missing parameter for the given tag.
+
+=cut
+
+sub new {
+    my ( $proto, $tag, $params ) = @_;
+    my $class = ref $proto || $proto;
+
+    if ( !exists $ERRORS{$tag} ) {
+        croak 'Unknown error tag.';
+    }
+
+    my $obj = { tag => $tag, params => {} };
+
+    if ( exists $ERRORS{$tag}->{arguments} ) {
+        foreach my $arg ( @{$ERRORS{$tag}->{arguments}} ) {
+            if ( !exists $params->{$arg} ) {
+                croak "Missing arguments $arg.";
+            }
+            $obj->{params}->{$arg} = $params->{$arg};
+        }
+    }
+
+    return bless $obj, $class;
+}
+
+
+=item message
+
+Returns the translated error message using the parameters given when creating the object.
+
+=cut
+
+sub message {
+    my ( $self ) = @_;
+    return __x $ERRORS{$self->{tag}}->{message}, %{$self->{params}};
+}
+
+
+=item tag
+
+Returns the message tag associated to the error.
+
+=cut
+
+sub tag {
+    my ( $self ) = @_;
+
+    return $self->{tag};
+}
+
+=item string
+
+Returns a string representation of the error object. Equivalent to message().
+
+=cut
+
+sub string {
+    my ( $self ) = @_;
+
+    return $self->message;
+}
+
+
+=back
+
+=cut
+
+1;