feat: plan MCP single-file module (building on jsonrpc)

[Oaklight]

Summary

Create an MCP (Model Context Protocol) single-file module for zerodep, leveraging the newly extracted jsonrpc module as its JSON-RPC 2.0 foundation.

Context

With the jsonrpc module now available as a shared dependency (#2), the MCP module can focus on MCP-specific protocol types, transport (stdio), and tool/resource/prompt primitives without reimplementing JSON-RPC 2.0.

Scope

• MCP protocol data types (Tool, Resource, Prompt, etc.)
• MCP-specific transport (stdio with Content-Length headers)
• Client and server implementations
• deps = ["jsonrpc"] in frontmatter

References

• MCP specification: https://modelcontextprotocol.io/specification
• jsonrpc module: jsonrpc/jsonrpc.py