No way to configure MCP server roots aka workspace folders.

I have a local HTTP MCP server which needs the client to assign file system root folder(s) as per the [MCP specification](https://modelcontextprotocol.io/specification/2025-11-25/client/roots) so the server can write files to the local file system.

The workspace gets added as root fine when using GitHub copilot in VS Code, but with the Copilot SDK I don't see any way to configure the roots that get passed to the server.
The configured copilot workspace folder is not automatically added as root either.

I'm using the SDK from .NET, but couldn't find any mentions of MCP roots in this repo in general.

首先在仓库中搜索 MCP 客户端配置，以及与服务器设置相关的 .NET SDK 入口点。将现有的 workspace 配置与 MCP roots 规范进行比较；完成的标准是调用方可以配置 roots，并且生成的 roots 会传递给服务器，包括已报告的 workspace 情况。

由索引模型根据 Issue 内容生成。