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/Address-TP/address02.md

@@ -0,0 +1,46 @@
+## ADDRESS02: Reverse DNS entry exists for name server IP address
+
+### Test case identifier
+**ADDRESS02** Reverse DNS entry should exist for name server IP address
+
+### Objective
+
+Some anti-spam techniques use reverse DNS lookup to allow incoming traffic.
+In order to prevent name servers to be blocked or blacklisted, DNS 
+administrators should publish PTR records associated to name server
+addresses.
+
+TODO: Technical reference to be found
+
+### Inputs
+
+The domain name to be tested.
+
+### Ordered description of steps to be taken to execute the test case
+
+1. Obtain the glue address records  of the domain checked
+   using [Method4](../Methods.md)
+
+2. Obtain the IP addresses of each name server of the domain checked
+   using [Method5](../Methods.md)
+
+3. For each IP address, a recursive PTR query must be performed.
+
+4. If any answer of the queries performed in step 3 contains an RCODE
+   other than NOERROR or if the answer does not include a PTR record,
+   this test case fails.
+
+### Outcome(s)
+
+If the test case succeeds, its result is a list of addresses with corresponding
+hostnames which are the result of the PTR queries performed.
+The result could be represented as a hash table where the keys are the IP
+addresses and the values their corresponding hostnames.
+
+### Special procedural requirements
+
+None.
+
+### Intercase dependencies
+
+The outcomes of this test is used as the input of [ADDRESS03](address03.md) test case.