Ability to set location of skills and mcp servers

### Feature summary

Button to set location of skills and mcp servers

### What problem are you trying to solve?

You can't set or change the location of global skills and MCP servers within the app, like you can for default location for repos. Currently it detects skills/MCP from C:\Users\\.copilot\ path (in windows).

Currently im duplicating skills in two directories to ensure the app picks it up.

### Proposed solution

A button to enable users to set the default location of skills, MCP servers etc.

### Workflow impact

All users affected.

Enable users to customise default location of more GitHub copilot configurations according to their preferences.

### Installation context

_No response_

### Additional context

_No response_

Issue 中没有指定文件、测试或入口点。首先定位现有的仓库默认位置设置，以及从 Windows 的 .copilot 路径发现全局 skills 和 MCP 服务器的代码；当用户可以在应用中配置位置，且发现功能不会产生重复 skills 时，即表示完成。

由索引模型根据 Issue 内容生成。