Fix registry publishing #102
Description
In .github/workflows/publish-nuget.yml we are attempting to publish to the MCP Registry using ./mcp-publisher publish --file=DotNetMcp/.mcp/server.json. However, this is failing because the --file parameter appears to be broken and may be removed (see modelcontextprotocol/registry#771).
An issue is that our server.json is dynamically generated to include version and path, and the NuGet publish requires the server.json file to be in the .mcp subdirectory.
As a workaround, the publish-nuget.yml workflow could copy server.json to the root so the publish step works. I think it should probably be deleted after the publish step completes since having two copies of this file in the repo seems error-prone but would like this decision to be evaluated.