mcpg-plugin-backend-mock

Mock backend binding plugin for mcpg — a developer/test fixture that returns a configured response without any external I/O. Supports a configured JSON `response` (wrapped as text + structured metadata), a `passthrough` mode that surfaces `response` as a literal CallToolResult (image/audio/embedded-resource/mixed content), a simulated `error` mode, and an optional `delay_ms`. Carries no transport machinery.