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/test-requirements/TestRequirements-table-specification.txt

@@ -0,0 +1,34 @@
+This document specifies the format of the table in document
+[TestRequirements.md] in the same directory. It is only relevant
+for anyone updating the table.
+
+The table in [TestRequirements.md] is also a database that
+should be parsable by script, and must therefore be kept in the
+specified format.
+
+The table, in the source code, must remain in Markdown format.
+In the raw Markdown code, the table must be preceded by an HTML
+comment line (with nothing in between) containing "START-TABLE".
+And directly after the table there must be an HTML comment
+containing "END-TABLE".
+
+The table must have four fields. There must be no "|" at the start
+or end of the lines in the table.
+
+Field one is the requirement ID which must have the form
+"Rxxxxx" where x is a digit 0-9. The ID should sorted and must be
+unique.
+
+Field two must be the requirement specification.
+
+Field three must be the requirement reference one or more
+Markdown links, i.e. something like "[xxxx]". The field may
+be empty.
+
+Field four must be one or more Markdown links to test cases.
+The field may be empty.
+
+The first line must be the table header and the second line
+the delimiter between header and table body. Both lines will be
+ignored by the parser.
+