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-gui/docs/README.md

@@ -0,0 +1,14 @@
+Zonemaster-GUI documents
+
+* An overview of the Zonemaster GUI is found in [Zonemaster UI]
+* Information related to code testing is found in [Unit testing Zonemaster-GUI]
+* [Installation instructions]
+* [Configuration instructions]
+* [Translation instructions]
+
+
+[Configuration instructions]:                     https://github.com/zonemaster/zonemaster/blob/master/docs/public/configuration/gui/README.md
+[Installation instructions]:                      https://doc.zonemaster.net/latest/installation/zonemaster-gui.html
+[Unit testing Zonemaster-GUI]:                    Testing.md
+[Translation instructions]:                       https://github.com/zonemaster/zonemaster/blob/master/docs/public/translation/Translating-GUI.md 
+[Zonemaster UI]:                                  UI.md

zonemaster-gui/docs/Testing.md

@@ -0,0 +1,46 @@
+# Unit testing of Zonemaster-GUI
+
+## Setup
+
+This part assumed that you have a working NodeJS environment on Ubuntu. See
+the [build environment] document for further instructions.
+
+The tests for Zonemaster GUI are implemented using [playwright], to install the
+tests dependencies run the following.
+
+```sh
+npm run e2e:install-deps
+npm run e2e:install
+```
+
+This will install system dependencies as well as the browsers used to tests the
+GUI.
+
+## Running the tests
+
+To run the tests run the following command.
+
+```sh
+npm run e2e
+```
+
+If the appearance of the GUI changes some tests might fail as the baseline for
+visual comparison is no longer up to date. In this case it is required to update
+the snapshots. The following commands updates the snapshots while ensuring a
+similar environment than the one the CI runs in is used (Ubuntu 22.04 and UTC
+time).
+
+```sh
+docker run --rm --network host -v $(pwd):/work/ -w /work/ -it mcr.microsoft.com/playwright:v1.57.0-jammy /bin/bash
+npm run e2e:install
+npm run e2e:update
+exit
+```
+
+Note that this method may not always work: it could happen that the generated
+snapshots are incorrect and have slight differences (e.g. appears zoomed in/out,
+etc). In that case, repeat the above steps but outside of the Docker environment,
+and preferably on a machine that uses a similar OS/environment as the CI.
+
+[build environment]: https://github.com/zonemaster/zonemaster/blob/master/docs/internal/distrib-testing/Ubuntu-Node.js-build-environment.md
+[playwright]: https://playwright.dev/docs/intro

zonemaster-gui/docs/TranslationGuide.md

@@ -0,0 +1 @@
+Moved to [translation documents](https://github.com/zonemaster/zonemaster/blob/develop/docs/public/translation/README.md).

zonemaster-gui/docs/UI.md

@@ -0,0 +1,54 @@
+# Zonemaster UI
+
+Zonemaster UI (Zonemaster-GUI) is a static website built with [Astro], using
+[Svelte] for interactive components and [Vite] for internationalization/translation
+(i18n).
+
+## Standalone Components
+
+Zonemaster UI also provides a set of standalone web components that can be
+reused in other projects. Currently, there are two available:
+
+- `<zm-domain-test>` – for initiating domain tests
+- `<zm-program-versions>` – displays the current versions of Zonemaster
+  components
+
+These components are framework-agnostic and can be embedded in other websites or
+apps as needed.
+
+```html
+<zm-domain-test></zm-domain-test>
+<zm-program-versions></zm-program-versions>
+
+<script type="module">
+    import '@zonemaster/ui';
+</script>
+```
+
+## Headless Mode
+
+Zonemaster UI can also be used in **headless mode**, where it acts as a
+JavaScript API layer between the Zonemaster backend and your own frontend.
+
+This is useful if you want to:
+
+- Build your own custom UI
+- Integrate Zonemaster functionality into another application or CLI tool
+
+In headless mode, the UI logic is decoupled from the visual components, allowing
+you to access core functionality programmatically through JavaScript.
+
+```ts
+import { TestAgent } from '@zonemaster/ui';
+
+TestAgent.subscribe((state, context) => {
+    console.log(state, context);
+});
+
+TestAgent.transition('START', { domain: 'example.com' });
+```
+
+
+[Astro]:      https://astro.build/
+[Svelte]:     https://svelte.dev/
+[Vite]:       https://vite.dev/