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/KNOWN_ISSUES

@@ -0,0 +1,12 @@
+We currently have the following known issues. They are all considered of low
+importance, and while we intend to fix them we make no promises about when.
+
+* When testing a zone using GOST-family algorithms in DNSSEC and having an
+  underlying OpenSSL library without GOST support, the Zonemaster DNSSEC test
+  results may be misleading or unpredictable. The Zonemaster::LDNS module will warn at
+  build time if OpenSSL lacks GOST support.
+  
+* Testing alternative root zones is not possible. Testing the usual root zone
+  is possible, but not all results make sense.
+  
+* Testing IDN names (U-label) does not always work.