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/maintenance/StyleGuide.md

@@ -0,0 +1,29 @@
+# Style Guide
+
+## Scope
+
+The following style guide applies to document text and certain file names
+specified below.
+
+## Guidelines
+
+* Zonemaster is always written as **Zonemaster**, never shortened (e.g. "ZM") or
+  uncapitalized (e.g. "zonemaster").
+* Case-insensitive regexes are always written out with the ignore-case flag
+  (e.g. `/[a-z]/i`).
+* For variable names in test case specifications each word is capitalized (e.g.
+  "Domain Part"). If a word is an abbreviation, it is usually written with all
+  capitals, e.g. "DNS".
+* When writing Markdown documents, use lower case fragments when referring to
+  internal headings' anchors, i.e. use `#objective` not `#Objective` to create
+  a link to the "Objective" section.
+* When linking to other documents and including the URL in the rendered text,
+  put angle brackets around the URL, i.e. use the [CommonMark autolink] syntax.
+  I.e. write as `<https://example.com/>` not just as `https://example.com/`.
+
+  If the angle brackets are not included the URL is still rendered as a link on
+  GitHub (per [GFM autolink] syntax), but other tools may not recognize it as a
+  link.
+
+[CommonMark autolink]: https://spec.commonmark.org/0.30/#autolinks
+[GFM autolink]: https://github.github.com/gfm/#autolinks-extension-