feat: Add MCP (Model Context Protocol) sample implementation

This commit adds a new MCP binding sample for UCP, enabling AI agents to
interact with UCP-compliant merchants through the Model Context Protocol.

New files:
- mcp/python/ucp_mcp_server.py: FastMCP server exposing UCP capabilities
  - Tools: list_products, create_checkout, add_to_checkout, complete_payment, etc.
  - Resources: catalog, checkout sessions, orders, discovery profile
  - Prompts: shopping assistant, order confirmation, product recommendations
  - Supports stdio, HTTP, and SSE transports

- mcp/python/ucp_mcp_client.py: Example client demonstrating complete shopping flow
  - Connects via MCP protocol
  - Demonstrates happy path: browse -> checkout -> pay -> track

- mcp/python/README.md: Comprehensive documentation
  - Architecture diagram
  - Quick start guide
  - Claude Desktop integration
  - Development guide

- mcp/python/pyproject.toml: Project configuration with dependencies

Updated:
- README.md: Added MCP binding section with comparison table

This sample enables conversational commerce experiences by allowing LLMs
like Claude, GPT, and Gemini to perform shopping operations through the
standardized MCP protocol.

Author: dihannahdi

README.md

@@ -21,7 +21,9 @@ Universal Commerce Protocol (UCP).
 
 ## Sample Implementations
 
-### Python
+### REST Bindings
+
+#### Python (REST)
 
 A reference implementation of a UCP Merchant Server using Python and FastAPI.
 
@@ -39,7 +41,7 @@ A reference implementation of a UCP Merchant Server using Python and FastAPI.
     *   A script demonstrating a full "happy path" user journey (discovery ->
         checkout -> payment).
 
-### Node.js
+#### Node.js (REST)
 
 A reference implementation of a UCP Merchant Server using Node.js, Hono, and
 Zod.
@@ -49,6 +51,41 @@ Zod.
     *   Demonstrates implementation of UCP specifications for shopping,
         checkout, and order management using a Node.js stack.
 
+### MCP Binding (Model Context Protocol)
+
+A reference implementation using the [Model Context Protocol](https://modelcontextprotocol.io/)
+for AI agent integration.
+
+*   **Server & Client**: [Documentation](mcp/python/README.md)
+
+    *   Located in `mcp/python/`.
+    *   Exposes UCP shopping capabilities as MCP tools and resources.
+    *   Enables AI agents (Claude, GPT, etc.) to perform commerce operations.
+    *   Includes example client demonstrating complete shopping flow.
+
+**Key Features:**
+*   Tools for product discovery, checkout, payment, and order management
+*   Resources for read-only access to catalogs, sessions, and orders
+*   Prompts for reusable conversation patterns
+*   Support for stdio, HTTP, and SSE transports
+
+### A2A Binding (Agent-to-Agent)
+
+An example Business A2A Agent implementing the UCP Extension.
+
+*   **Agent & Client**: [Documentation](a2a/README.md)
+    *   Located in `a2a/`.
+    *   Demonstrates agent-to-agent communication for commerce operations.
+    *   Includes chat client for interactive testing.
+
+## Protocol Binding Comparison
+
+| Binding | Use Case | Transport | Best For |
+|---------|----------|-----------|----------|
+| REST | Traditional APIs | HTTP | Web/mobile apps, service integration |
+| MCP | AI Agents | stdio/HTTP/SSE | LLM integration, conversational commerce |
+| A2A | Agent Communication | HTTP | Multi-agent systems, automated workflows |
+
 ## Getting Started
 
 Please refer to the specific README files linked above for detailed instructions