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/00-load.t

@@ -0,0 +1,12 @@
+use 5.014002;
+use strict;
+use warnings FATAL => 'all';
+use Test::More;
+
+plan tests => 1;
+
+BEGIN {
+    use_ok( 'Zonemaster::Backend::Config' ) || print "Bail out!\n";
+}
+
+done_testing;