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/development/README.md

@@ -0,0 +1,9 @@
+# Zonemaster development guide
+
+The development guide provides instructions for various tasks related to the
+development of each component of Zonemaster.
+
+Development guides:
+ * [Zonemaster-CLI development]
+
+[Zonemaster-CLI development]: cli.md

zonemaster/docs/public/development/cli.md

@@ -0,0 +1,17 @@
+# Development
+
+## Overview
+
+This is the development guide for Zonemaster-CLI.
+It provides instructions for various tasks related to the development of
+Zonemaster-CLI.
+
+## Common Developer Actions
+
+### Generate man page
+
+To generate and view a development version of the man page:
+
+```sh
+perldoc -oman script/zonemaster-cli
+```