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/Zone-TP/zone05.md

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+## ZONE05: SOA 'expire' minimum value
+
+### Test case identifier
+**ZONE05** SOA 'expire' minimum value
+
+### Objective
+
+The SOA expire value specifies for how long any secondary name server
+keeps the zone valid without any contact with the primary name server.
+This value should be greater than how long a major outage would
+typically last. The expire value should also be larger than the
+refresh and retry values, as described in section 3.3.13 in
+[RFC 1035](https://datatracker.ietf.org/doc/html/rfc1035), and clarified in
+section 2.2 of [RFC 1912](https://datatracker.ietf.org/doc/html/rfc1912).
+
+Setting the expire value low will increase the risk of any unwanted
+non-availability of the zone because of any failures in contacting
+the primary name server.
+
+The [RIPE-203](https://www.ripe.net/publications/docs/ripe-203) recommendation
+for the expire value is 1000 hours (roughly 41 days). Older DNSCheck code
+had a 7 day minimum value (604800 seconds), and this is the minimum
+value we recommend as an absolute minimum.
+
+### Inputs
+
+The domain name to be tested.
+
+### Ordered description of steps to be taken to execute the test case
+
+1. Retrieve the SOA record from a delegated name server for the domain.
+2. If the answer from step 1 is not authoritative, iterate step 1 until there is an authoritative answer.
+3. Retrieve the expire value and the refresh value from the SOA record.
+4. If the expire value is less than 604800 seconds (7 days), this test
+   case fails.
+5. If the expire value is lower than the refresh value, this test case
+   fails.
+
+### Outcome(s)
+
+If the expire value is less than 604800 seconds or if the expire value is
+lower than the refresh value, this test case fails.
+
+### Special procedural requirements
+
+None.
+
+### Intercase dependencies
+
+None.