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/upgrading/backend.md

@@ -0,0 +1,78 @@
+# Upgrade Backend
+
+## 1. Overview
+
+This document contains pointer to instructions on how to upgrade the
+Zonemaster::Backend component. An upgrade usually consist of an upgrade script
+to upgrade the database, and instructions to install new dependencies.
+
+> When upgrading from a version < v6.2.0 to a version ≥ v8.0.0, it is
+> recommended to install the desired version following the [Installation
+> instructions] skipping the part about the database if you want to keep it. To
+> upgrade the database, apply each upgrade instructions one after another (see
+> table below).
+
+## 2. Prerequisites
+
+Upgrade Zonemaster::LDNS and Zonemaster::Engine first following instructions
+within the [Zonemaster::Engine installation] document.
+
+## 3. Upgrading Zonemaster::Backend
+
+To upgrade Zonemaster::Backend perform the following tasks:
+
+  1. stop the `zm-rpcapi` and `zm-testagent` daemons (`zm_rpcapi` and
+     `zm_testagent` on FreeBSD)
+  2. remove old files with `cpanm --uninstall Zonemaster::Backend`
+  3. install any new dependencies (see corresponding upgrade document below)
+  4. install the latest version from CPAN with `cpanm Zonemaster::Backend`
+  5. apply any remaining instructions specific to this new release
+  6. start the `zm-rpcapi` and `zm-testagent` daemons (`zm_rpcapi` and
+     `zm_testagent` on FreeBSD)
+
+
+### Specific upgrade instructions
+
+> Always make a backup of the database before upgrading it.
+
+When upgrading Zonemaster::Backend, it might be needed to upgrade the database
+and/or install new dependencies. Such instructions are available in the upgrade
+document coming with the release. See table below to refer to the right
+document.
+
+*When upgrading from an older version than the previous release, apply each
+upgrade instructions one after another.*
+
+Current Zonemaster::Backend version | Link to instructions | Comments
+------------------------------------|----------------------|-----------------------
+ version < 1.0.3                    | [Upgrade to 1.0.3]   |
+ 1.0.3 ≤ version < 1.1.0            | [Upgrade to 1.1.0]   |
+ 1.1.0 ≤ version < 5.0.0            | [Upgrade to 5.0.0]   |
+ 5.0.0 ≤ version < 5.0.2            | [Upgrade to 5.0.2]   | For MySQL/MariaDB only
+ 5.0.2 ≤ version < 8.0.0            | [Upgrade to 8.0.0]   |
+ 8.0.0 ≤ version < 9.0.0            | [Upgrade to 9.0.0]   |
+ 9.0.0 ≤ version < 11.1.0           | [Upgrade to 11.1.0]  |
+ 11.1.0 ≤ version < 11.2.0          | [Upgrade to 11.2.0]  |
+ 11.2.0 ≤ version                   | -                    | No special steps needed for upgrade
+
+## 4. Find current version
+
+The following command will report the version of Zonemaster-Backend currently
+installed. If an error is report Zonemaster-Backend is not installed or not
+available for the user. If so, consider tunning the command as root or with
+`sudo`.
+
+```sh
+perl -E 'use Zonemaster::Backend; say $Zonemaster::Backend::VERSION;'
+```
+
+[Installation instructions]: ../installation/zonemaster-backend.md
+[Upgrade to 1.0.3]:          backend/upgrade_zonemaster_backend_ver_1.0.3.md
+[Upgrade to 1.1.0]:          backend/upgrade_zonemaster_backend_ver_1.1.0.md
+[Upgrade to 5.0.0]:          backend/upgrade_zonemaster_backend_ver_5.0.0.md
+[Upgrade to 5.0.2]:          backend/upgrade_zonemaster_backend_ver_5.0.2.md
+[Upgrade to 8.0.0]:          backend/upgrade_zonemaster_backend_ver_8.0.0.md
+[Upgrade to 9.0.0]:          backend/upgrade_zonemaster_backend_ver_9.0.0.md
+[Upgrade to 11.1.0]:         backend/upgrade_zonemaster_backend_ver_11.1.0.md
+[Upgrade to 11.2.0]:         backend/upgrade_zonemaster_backend_ver_11.2.0.md
+[Zonemaster::Engine installation]: ../installation/zonemaster-engine.md