Function mergeMcpJson

mergeMcpJson(
existing: Record<string, unknown>,
): { changed: boolean; config: Record<string, unknown> }
Merge the stone server into an existing .mcp.json object without clobbering anything.

It only adds the stone entry when absent, so a developer's own config (other servers, or a customized stone entry) is preserved.
Parameters
- existing: Record<string, unknown>
  The parsed .mcp.json (or undefined when the file does not exist).
Returns { changed: boolean; config: Record<string, unknown> }
The merged config and whether it changed.