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/Syntax-TP/README.md

@@ -0,0 +1,25 @@
+# Syntax Test Plan
+
+These are tests of the syntax of different labels in DNS, such as domain
+names and host names.
+
+This document uses the terminology defined in the [Master Test Plan].
+
+
+[Master Test Plan]:             ../MasterTestPlan.md
+[Test Case README]:             ../README.md
+
+<!-- Content until EOF generated by script updateTestPlanReadme.pl from Zonemaster/Zonemaster utils directory -->
+
+## Test cases list
+
+|Test Case |Test Case Description|
+|:---------|:--------------------|
+|[SYNTAX01](syntax01.md)|No illegal characters in the domain name|
+|[SYNTAX02](syntax02.md)|No hyphen ('-') at the start or end of the domain name|
+|[SYNTAX03](syntax03.md)|There must be no double hyphen ('--') in position 3 and 4 of the domain name|
+|[SYNTAX04](syntax04.md)|The NS name must have a valid domain/hostname|
+|[SYNTAX05](syntax05.md)|Misuse of '@' character in the SOA RNAME field|
+|[SYNTAX06](syntax06.md)|No illegal characters in the SOA RNAME field|
+|[SYNTAX07](syntax07.md)|No illegal characters in the SOA MNAME field|
+|[SYNTAX08](syntax08.md)|MX name must have a valid hostname|