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/nameserver06.md

@@ -0,0 +1,47 @@
+## NAMESERVER06: NS can be resolved
+
+### Test case identifier
+**NAMESERVER06** NS can be resolved
+
+### Objective
+
+All name servers names listed for a delegation must be resolvable in DNS.
+If they are not resolvable using DNS this is a sign of misconfiguration,
+and raises the risk of unreachability for the domain. It could also lower
+the performance for any resolver trying to resolve the name.
+
+The objective of this test is to resolve the domain using all the listed
+name servers used in the delegation. More information about resolver
+behavior is in section 7 of [RFC 1035](https://datatracker.ietf.org/doc/html/rfc1035).
+
+### Inputs
+
+The domain name to be tested.
+
+### Ordered description of steps to be taken to execute the test case
+
+1. Obtain the list of name servers for the domain using [Method 2](
+   ../Methods.md#method-2-obtain-glue-name-records-from-parent) and [Method 3](
+   ../Methods.md#method-3-obtain-name-servers-from-child).
+2. Use [Method 4](
+   ../Methods.md#method-4-obtain-glue-address-records-from-parent) and
+   [Method 5](
+   ../Methods.md#method-5-obtain-the-name-server-address-records-from-child)
+   to resolve all the name server names obtained in step 1.
+3. If any name does not resolve to either an A RR or AAAA RR, this test
+   case fails.
+
+### Outcome(s)
+
+If any of the name server names fails to resolve to an IP address, this
+test case fails.
+
+### 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.