Add mcp server

[haixuanTao]

This is a quick rewrite of our existing openai realtime script as an mcp server that can be configured with:

{
  "servers": {
    "reachy": {
      "command": "uv",
      "args": [
        "--directory",
        "/path/to/reachy_mini_conversation_demo",
        "run",
        "reachy-mini-mcp"
      ],
    }
  }
}

And then let the llm mcp tool call Reachy Mini. :)

I have reduced the number of tools in order for lower latency on local llm but we can add more in the future!