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/CONTRIBUTE.md

@@ -0,0 +1,66 @@
+# Contribute
+
+Thank you for considering contributing to Zonemaster GUI! This document provides guidelines for contributing to the project.
+
+## Project Overview
+
+Zonemaster GUI is built with:
+- [Astro](https://astro.build/) as the main framework
+- [Svelte](https://svelte.dev/) for UI components
+- [TypeScript](https://www.typescriptlang.org/) for type safety
+
+## Development Setup
+
+1. Clone the repository
+2. Install dependencies:
+   ```bash
+   npm install
+   ```
+3. Start the development server:
+   ```bash
+   npm run dev
+   ```
+
+## Code Style
+
+We use [Prettier](https://prettier.io/) for code formatting with the following configuration:
+- Single quotes
+- 4 spaces for indentation
+- No tabs
+
+To format your code:
+```bash
+npx prettier --write .
+```
+
+## Testing
+
+We use [Playwright](https://playwright.dev/) for end-to-end testing. Tests are located in the `e2e` directory.
+
+To run tests:
+```bash
+npm run e2e
+```
+
+## GUI Modifications
+
+Zonemaster GUI is designed to be cloned and customized for theming purposes. When making changes to the GUI, please be mindful of the following:
+
+- **Be careful when renaming CSS class names** - Many themes may depend on these class names
+- **Avoid deleting, renaming, or moving template files** without proper deprecation notices
+- **Consider backward compatibility** when modifying component structures
+- **Document any breaking changes** that might affect custom themes
+
+While it's ultimately up to theme creators to handle conflicts when syncing with the main repository, we should minimize disruption where possible. For more information on theming, see the [THEMING.md](docs/THEMING.md) document.
+
+## Pull Request Process
+
+1. Fork the repository
+2. Create a feature branch
+3. Make your changes
+4. Ensure tests pass
+5. Submit a pull request
+
+## Code of Conduct
+
+Please be respectful and considerate of others when contributing to this project.