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/public/configuration/README.md

@@ -0,0 +1,17 @@
+# Configuration
+
+This section contains information about configuration of the different components
+of Zonemaster:
+
+* Setting up or modifying the [profile] in Zonemaster-Engine.
+* Enabling the Zonemaster-Engine [global cache] feature.
+* Configuring Zonemaster-Backend in the [Backend configuration file].
+* Using [environment variables] for Zonemaster-Backend.
+* Configuring Zonemaster-GUI in the [GUI configuration section].
+
+
+[profile]:                      profiles.md
+[global cache]:                 global-cache.md
+[Backend configuration file]:   backend.md
+[environment variables]:        backend-environment-variables.md
+[GUI configuration section]:    gui/README.md