New MCP tool for renoise

[kunitoki]

This pull request introduces the initial implementation of the Renoise MCP (Model Context Protocol) server tool, making Renoise controllable by AI clients such as Claude Desktop and Claude Code. It adds a complete, self-contained Renoise tool package with documentation, manifest, entry point, a pure Lua JSON encoder/decoder, and an extensible tool registry and protocol handler. The server exposes Renoise’s full song API over HTTP for AI-driven music composition and editing.

The most important changes are:

Documentation and Manifest:

• Added a comprehensive README.md describing installation, usage, supported commands, architecture, and extension points for the Renoise MCP tool.
• Added manifest.xml with tool metadata for Renoise, including API version, author, and description.

Core Architecture and Entry Point:

• Introduced main.lua as the entry point, registering menu entries and keybindings to launch the MCP server control panel within Renoise.

JSON and Protocol Handling:

• Implemented a pure Lua JSON encoder/decoder in mcp/json.lua, ensuring compatibility with Renoise’s Lua environment and no external dependencies.
• Added mcp/router.lua, which loads tool definitions, registers them, and handles all MCP protocol requests, including tool listing, invocation, and error handling. This enables extensibility by simply adding .lua files in the tools/ directory.