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/configuration/gui/configuring-using-tsconfig-json.md

@@ -0,0 +1,81 @@
+# Advanced build-time configuring Zonemaster-GUI using "tsconfig.json"
+
+The `tsconfig.json` configuration file can be used for *build-time* settings of
+Zonemaster-GUI. Any changes to this file require a rebuild of the installation
+package.
+
+## Finding "tsconfig.json"
+
+In the source tree the file is found as `tsconfig.json` relative to the root of
+the Git tree. It does not exist in the installed Zonemaster-GUI, as the values
+have been built-in.
+
+## Rebuilding Zonemaster-GUI after update
+
+When `tsconfig.json` has been updated, Zonemaster-GUI has to be rebuilt. See
+[building installation package] for how to get the source tree and building a new
+installation package.
+
+## Default "tsconfig`.json"
+
+The `tsconfig.json` file is a TypeScript configuration file that includes path
+aliases like `@theme/*` to simplify imports and make theming more manageable.
+
+
+```json
+{
+  "extends": "astro/tsconfigs/strict",
+  "include": [".astro/types.d.ts", "**/*"],
+  "exclude": ["dist"],
+  "compilerOptions": {
+    "baseUrl": ".",
+    "paths": {
+      "@/*": ["./src/*"],
+      "@theme/*": ["./src/themes/default/*"]
+    },
+    "resolveJsonModule": true,
+    "esModuleInterop": true
+  }
+}
+```
+
+## @theme/* Alias in "tsconfig.json"
+
+The path alias configuration allows importing from the default theme directory
+using the `@theme` prefix, which makes it possible to create a customize the
+look-and-feel of the Zonemaster-GUI, e.g. set other colors and type faces.
+
+```json
+{
+  "paths": {
+    "@/*": ["./src/*"],
+    "@theme/*": ["./src/themes/default/*"]
+  }
+}
+```
+
+This alias makes it easier to import theme-specific components and styles
+in your code. For example, instead of writing:
+
+```typescript
+import Button from '../../themes/default/components/Button';
+```
+
+You can use:
+
+```typescript
+import Button from '@theme/components/Button';
+```
+
+This approach simplifies imports and makes it easier to switch between different
+themes by changing the alias path.
+
+
+## Theming
+
+In the [Theming Zonemaster-GUI] document you will find instructions how to add
+custom theming to Zonemaster-GUI.
+
+
+[Building installation package]:                 building-custom-gui.md
+[Theming Zonemaster-GUI]:                        https://github.com/zonemaster/zonemaster-gui/blob/master/docs/theming-zonemaster-gui.md