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/nameserver04.md

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+## NAMESERVER04: Same source address
+
+### Test case identifier
+**NAMESERVER04** Same source address
+
+### Objective
+
+Responses from the authoritative name servers must contain same source IP
+address as the destination IP address of the initial query. This has been
+clarified in section 4 of
+[RFC 2181](https://datatracker.ietf.org/doc/html/rfc2181#section-4).
+
+### 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. A SOA query for the domain name sent to the each name server IP address 
+   found in step 1.
+3. Any answer received from the SOA query must come from the same source IP address
+   as the query was sent to. If there is a mismatch, this test case fails.
+
+### Outcome(s)
+
+If any response comes from another IP address than the query was sent to,
+this test case fails.
+
+### Special procedural requirements
+
+If there are many authoritative DNS nodes behind the IP address the query
+is sent to, there could be multiple answers with possibly different source
+addresses for the query. This special case is currently ignored.
+
+### Intercase dependencies
+
+None.