Unclear schema for fixed (constant) CLI arguments #169

Describe the bug

Suppose you have an MCP server that has mcp start as required CLI arguments. Perhaps the MCP server is a CLI tool package with multiple purposes, not just MCP and mcp start invokes the MCP server subroutine.

I believe these would be expressed as positional arguments with a value. But value_hint is required.

VS Code appears to prefer value and tolerate a missing value_hint:
https://github.com/microsoft/vscode/blob/1ea38ea6831a8c05cb071e9219f11ad546b1b748/src/vs/platform/mcp/common/mcpManagementService.ts#L275-L281

So perhaps value_hint can become optional? Or maybe we need a ConstantArgument which has a required value and type = constant but no name or runtime_hint?

To Reproduce

Here is a sample server.json that shows the clunkiness.

{
  "description": "A sample MCP server using the MCP C# SDK. Generates random numbers and random weather.",
  "name": "io.github.joelverhagen/Knapcode.SampleMcpServer",
  "packages": [
    {
      "registry_name": "nuget",
      "name": "Knapcode.SampleMcpServer",
      "version": "0.4.0-beta",
      "package_arguments": [
        {
          "type": "positional",
          "value_hint": "mcp",
          "value": "mcp"
        },
        {
          "type": "positional",
          "value_hint": "start",
          "value": "start"
        }
      ]
    }
  ],
  "version_detail": {
    "version": "0.4.0-beta"
  }
}

Expected behavior

There should be clear guidance on fixed (non-input) positional arguments.