Antigravity expects "disabled": true in mcp_config.json rather than
"enabled": false. Map disabled servers to disabled = true and strip
the unrecognized enabled attribute.
Do not serialize null/empty fields (command, args, env) for remote servers.
Also fix 'isRemote' check to check for non-null url fields instead of
using the ? operator, which evaluates to true even if the key is null.
Do not rename url to serverUrl in transformMcpServer's extraTransforms.
This caused the core library to incorrectly default the server type to stdio,
and subsequently erase the serverUrl attribute entirely during cleanup.
The renaming is already handled at the end by the transformMcpServers helper.
