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/specifications/tests/Nameserver-TP/nameserver03.md

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+## NAMESERVER03: Test availability of zone transfer (AXFR)
+
+### Test case identifier
+**NAMESERVER03** Test availability of zone transfer (AXFR)
+
+### Objective
+
+AXFR is a mechanism to transfer the whole content of a zone from a name
+server. Some people prefer to not disclose the whole content of a zone
+for various reasons, and thus wants the public name server infrastructure
+not do disclose the whole zone content to the public. This test case
+checks the availability of the AXFR mechanism.
+
+AXFR is defined in its latest revision in
+[RFC 5936](https://datatracker.ietf.org/doc/html/rfc5936).
+
+### Inputs
+
+The domain name to be tested.
+
+### Ordered description of steps to be taken to execute the test case
+1. Retrieve all address records for all the name servers using [Method 
+   4](../Methods.md) and [Method 5](../Methods.md).
+2. Send an AXFR query to each name server IP address found in step 1.
+3. If any answer to the AXFR query is starting with the SOA record
+   for the domain, this test case fails.
+
+### Outcome(s)
+
+If any name server for the domain allows a zone transfer using AXFR,
+this test case fails.
+
+### Special procedural requirements
+
+None.
+
+### Intercase dependencies
+
+None.