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-gui/docs/README.md

@@ -0,0 +1,14 @@
+Zonemaster-GUI documents
+
+* An overview of the Zonemaster GUI is found in [Zonemaster UI]
+* Information related to code testing is found in [Unit testing Zonemaster-GUI]
+* [Installation instructions]
+* [Configuration instructions]
+* [Translation instructions]
+
+
+[Configuration instructions]:                     https://github.com/zonemaster/zonemaster/blob/master/docs/public/configuration/gui/README.md
+[Installation instructions]:                      https://doc.zonemaster.net/latest/installation/zonemaster-gui.html
+[Unit testing Zonemaster-GUI]:                    Testing.md
+[Translation instructions]:                       https://github.com/zonemaster/zonemaster/blob/master/docs/public/translation/Translating-GUI.md 
+[Zonemaster UI]:                                  UI.md