Expose the P2P API as MCP server tools

[dotnetspark]

Summary

Add an MCP server layer that exposes the existing P2P API workflows as agent-callable tools.

Goal

Treat the current REST API as the system of record and add an MCP tool surface that makes the repo usable from general agent runtimes, with LangGraph as one possible consumer rather than the defining interface.

Scope

• specify an MCP server feature for the existing P2P workflows
• plan contracts, tool surface, and execution model
• generate tasks and implement the feature
• preserve the existing HTTP API as the underlying business interface

Initial direction

• expose tools for purchase-order creation, submission, receiving, querying
• expose tools for invoice creation, matching, approval, payment
• expose tools for vendor exposure and credit-check status
• keep the MCP layer thin and deterministic over the existing service behavior