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/internal/functional-tests/Behavior-TP/behavior01.md

@@ -0,0 +1,35 @@
+## BEHAVIOR01: NXDOMAIN returned in response in the event of querying a domain name that does not exist
+
+### Test case identifier
+
+**BEHAVIOR01:** Name Error RCODE returned in response in the event of
+querying a domain name that does not exist
+
+### Objective 
+This test is to verify whether the engine responds with a RCODE NXDOMAIN when
+querying a domain name that does not exist.
+
+### Inputs
+
+The domain to be tested. The domain should not be already delegated in the DNS.
+
+### Ordered description of steps to be taken to execute the test case
+
+1. Zonemaster CLI is used to verify an invalid domain
+2. If the query don’t receive an RCODE NXDOMAIN, the test returns FAIL
+
+
+### Results
+Verifying the invalid domain with zonemaster CLI does provide conclusive errors as you
+could see from the appendix
+
+### Appendix
+```
+zonemaster-cli afnics.fr
+Seconds Level     Message
+======= ========= =======
+   1.17 CRITICAL  Nameserver for zone fr responded with NXDOMAIN to query for
+glue.
+   1.17 CRITICAL  Not enough data about afnics.fr was found to be able to run
+tests.
+```