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/Delegation-TP/delegation06.md

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+## DELEGATION06: Existence of SOA
+
+### Test case identifier
+
+**DELEGATION06:** Existence of SOA
+
+### Objective
+
+Section 6.1 of the [RFC 2181](https://datatracker.ietf.org/doc/html/rfc2181) specifies
+that the SOA record is mandatory for every zone. 
+
+This test is intended to verify the presence of a SOA record for the
+domain.
+
+### Inputs
+
+The domain name to be tested.
+
+### Ordered description of steps to be taken to execute the test case
+
+1. Obtain the complete set of name server address records from the parent using
+   [Method4](../Methods.md) and the child using [Method5](../Methods.md).
+2. All the uniquely obtained address records are queried for the SOA record.
+3. If there is an answer with NOERROR and there is no content in the
+   answer section, this test case fails.
+
+### Outcome(s)
+
+If there is a SOA record present for the domain this test case succeeds.
+
+### Special procedural requirements
+
+If either IPv4 or IPv6 transport is disabled, ignore the evaluation of the
+result of any test using this transport protocol. Log a message reporting
+on the ignored result.
+
+### Intercase dependencies
+
+None