MCP usage across features and request routing

[jeffpaul]

Description

Expand and validate the plugin’s use of the Model Context Protocol (MCP) for routing AI requests and discovering provider capabilities. This ensures the AI Experiments plugin demonstrates best practices for integrating both the WP AI Client SDK and its underlying PHP AI Client SDK across different features and providers.

Goals

• Implement MCP-based routing for at least one feature (for example, Alt Text Generation or Content Summarization).
• Create a reusable adapter layer that standardizes how MCP connections are established and used by feature modules.
• Demonstrate how MCP can simplify capability discovery, provider switching, and performance monitoring.
• Document when and why to use MCP versus direct SDK calls in /docs/mcp-adapters.md.
• Validate that both the WP AI Client SDK and the underlying PHP AI Client SDK can interoperate smoothly via MCP.

Acceptance Criteria

• At least one feature successfully executes AI requests via MCP.
• Common adapter pattern implemented and reusable by other features.
• MCP usage documented and tested with at least two providers.
• No regressions in direct SDK features when MCP is active.
• Documentation clearly explains when to use each integration path.