feat: add graphify-mcp console script entry point

[jr2804]

Summary

This PR adds a graphify-mcp console script entry point, making the MCP stdio server directly invocable as a first-class CLI command.

Motivation

When graphifyy is installed via isolated package managers such as uv tool install or pipx, the module graphify.serve is not available to the user's default python interpreter. The current recommended invocation python -m graphify.serve graphify-out/graph.json therefore fails in these environments because python cannot find the graphify module.

By exposing graphify.serve:_main as a dedicated graphify-mcp script:

• uv tool install graphifyy[mcp] or pipx install graphifyy[mcp] can directly expose graphify-mcp on $PATH
• MCP server configurations (e.g. Claude Code, VS Code Copilot) can reference graphify-mcp as a stable command rather than relying on python -m graphify.serve
• Users do not need to know the internal module path to start the server

Change

[project.scripts]
graphify = "graphify.__main__:main"
graphify-mcp = "graphify.serve:_main"

The new graphify-mcp command accepts the same arguments as python -m graphify.serve (e.g. graphify-mcp graphify-out/graph.json).

Checklist

• Single-line change to [project.scripts] in pyproject.toml
• Uses existing _main() entry point already defined in graphify.serve
• No new runtime dependencies or breaking changes