Can't send inline json with additional-mcp-config flag

### Describe the bug

I'm trying to add inline json with the additional-mcp-config flag. It seems that the JSON parsing dies on the second character no matter what I do, so I can't even get to the point of configuring my actual MCP server.
I assume escaping quotes is the problem, but I've tried multiple ways around it with no luck. The following command fails in Windows powershell:

```
npx -y @github/copilot@latest --additional-mcp-config '{"mcpServers":{}}'
```

Output:
```
Invalid JSON in --additional-mcp-config: Expected property name or '}' in JSON at position 1 (line 1 column 2)
```

### Affected version

0.0.353

### Steps to reproduce the behavior

1. In windows powershell, run `npx -y @github/copilot@latest --additional-mcp-config '{mcpServers:{}}'`

### Expected behavior

Copilot is launched. I have an actual mcp server config in my case, but it doesn't launch even if I pass an empty set of servers.

### Additional context

- Happens with powershell via windows terminal or directly opening powershell.