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/docs/README.md

@@ -0,0 +1,19 @@
+# Documentation
+
+In this repository, most documentation of Zonemaster is found.
+
+* [public] - In the public documentation you will find installation instructions,
+  user guides for each Zonemaster component and other documentation.
+* [internal] - In the internal tree you can find documentation regarding the
+  design and requirements of the Zonemaster implementation.
+* [Contact and Mailing lists] - Information on forum and mailing lists for
+  Zonemaster.
+
+The [public] documentation can be built using [mdbook]. See
+[public/README][public] for details.
+
+
+[Contact and Mailing lists]:           contact-and-mailing-lists.md
+[Internal]:                            ./internal
+[mdbook]:                              https://rust-lang.github.io/mdBook/
+[Public]:                              ./public/README.md