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/lib/Zonemaster/Backend/Metrics.pm

@@ -0,0 +1,60 @@
+package Zonemaster::Backend::Metrics;
+
+use strict;
+use warnings;
+
+use Log::Any qw($log);
+
+eval("use Net::Statsd");
+
+my $enable_metrics = 0;
+
+if (!$@) {
+    $enable_metrics = 1;
+}
+
+my %CODE_STATUS_HASH = (
+    -32700 => 'RPC_PARSE_ERROR',
+    -32600 => 'RPC_INVALID_REQUEST',
+    -32601 => 'RPC_METHOD_NOT_FOUND',
+    -32602 => 'RPC_INVALID_PARAMS',
+    -32603 => 'RPC_INTERNAL_ERROR'
+);
+
+sub setup {
+    my ( $cls, $host, $port ) = @_;
+    if (!defined $host) {
+        $enable_metrics = 0;
+    } elsif ( $enable_metrics ) {
+        $log->info('Enabling metrics module', { host => $host, port => $port });
+        $Net::Statsd::HOST = $host;
+        $Net::Statsd::PORT = $port;
+    }
+}
+
+sub code_to_status {
+    my ($cls, $code) = @_;
+    if (defined $code) {
+        return $CODE_STATUS_HASH{$code};
+    } else {
+        return 'RPC_SUCCESS';
+    }
+}
+
+sub increment {
+    if ( $enable_metrics ) {
+        Net::Statsd::increment(@_);
+    }
+}
+
+sub gauge {
+    if ( $enable_metrics ) {
+        Net::Statsd::gauge(@_);
+    }
+}
+
+sub timing {
+    if ( $enable_metrics ) {
+        Net::Statsd::timing(@_);
+    }
+}