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/Restriction-TP/restriction01.md

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+## RESTRICTION01: Label length
+
+### Test case identifier
+
+**RESTRICTION01:** Label length
+
+### Objective
+In DNS, domain names are expressed in terms of a sequence of labels. Section 
+2.3.1 of [RFC 1035](https://datatracker.ietf.org/doc/html/rfc1035) mentions that the 
+label must be 63 characters or less.
+
+The objective for this test is verify whether the engine conforms to the
+specification described in the previous paragraph.
+
+### Results
+Since it is not possible to fit in more than 63 octets in a DNS label
+, it is impossible to run this test. 

zonemaster/docs/internal/functional-tests/Restriction-TP/restriction02.md

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+## RESTRICTION02: Domain name length
+
+### Test case identifier
+
+**RESTRICTION02:** Domain name length
+
+### Objective
+Section 3.1 of [RFC 1035](https://datatracker.ietf.org/doc/html/rfc1035) mentions that the
+the total length of a domain name (i.e., label octets and label length octets) 
+is restricted to 255 octets or less.
+
+The objective for this test is verify whether the engine conforms to the
+specification described in the previous paragraph
+
+### Results
+Since it is not possible to fit in more than 255 octets in a DNS 
+packet, this test is not run.

zonemaster/docs/internal/functional-tests/Restriction-TP/restriction03.md

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+## RESTRICTION03: Character set restriction for label
+
+### Test case identifier
+
+**RESTRICTION03:** Character set restriction for label
+
+### Objective
+
+Even though section 11 of [RFC 2181](https://datatracker.ietf.org/doc/html/rfc2181) mentions 
+that any binary string could be part of a label, many of the registries will
+not permit special symbols in the label. This is an habit pursued by the
+registries based on section 2.1 of the [RFC 1123](https://datatracker.ietf.org/doc/html/rfc1123),
+i.e. following the LDH (Letters, Digits and Hyphen) format. Even for the
+IDNs [RFC 5892](https://datatracker.ietf.org/doc/html/rfc5892) limits to the LDH
+format.
+
+The objective for this test is verify whether the engine identifies the
+domain names which is not in the LDH format. 
+
+### Result
+
+The engine does not capture the restriction for LDH and the explanation is
+provided here : https://github.com/zonemaster/zonemaster/issues/153 
+