Add AI demo

Problem/Motivation

We need to provide a ready-to-use AI demo on Drupal Forge. Keys will be provided with environment variables so users do not have to enter them. We need keys that can be assigned limited funds to control costs.

Proposed resolution

Set up Drupal CMS demo template with the drupal_cms_ai recipe applied. Use OpenRouter to generate $0.25 keys and assign to openai_api_key environment variable.

Remaining tasks

User interface changes

API changes

Data model changes