Add Composer installation instructions for KumbiaPHP

[henrystivens]

• Include steps for installing KumbiaPHP using Composer.
• Provide commands for creating a project and starting the development server.

[Copilot]

Pull Request Overview

This PR adds Composer installation instructions to the Spanish KumbiaPHP documentation. It provides an alternative installation method using PHP's standard dependency manager alongside the existing manual installation instructions.

• Adds a new "Instalación con Composer" section with step-by-step instructions
• Includes commands for project creation, navigation, and development server startup
• Provides browser access instructions for verifying the installation

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_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[Copilot]

The script path ./bin/phpserver may not be correct for a Composer-installed KumbiaPHP project. Verify that this script exists at this location in the project structure created by composer create-project kumbia/framework. Consider providing the actual path or an alternative command like php -S 127.0.0.1:8001 if the script doesn't exist.

Suggested change

	./bin/phpserver
	```
	Este comando levantará un servidor local con el puerto **8001** por defecto.
	php -S 127.0.0.1:8001 -t default/public

Este comando levantará un servidor local en el puerto 8001 y usará el directorio default/public como raíz del documento.