Document real-world usage of Abilities API and MCP Adapter

[jeffpaul]

Add documentation demonstrating how the Abilities API and MCP Adapter are used in practice within the AI Experiments plugin. This should go beyond API descriptions and show real integration examples.

Acceptance criteria:

• Documentation includes real, concrete examples from the plugin
• Examples cover both Abilities API and MCP Adapter usage
• Content is suitable for developers evaluating how to build on these systems
• Documentation clearly connects concepts to working code