meshagentBaseUrl function
Return the base URL for meshagent, checking environment variables first.
Implementation
String meshagentBaseUrl([String? baseUrl]) {
  // If baseUrl is already provided, just return it.
  if (baseUrl != null && baseUrl.isNotEmpty) {
    return baseUrl;
  }
  // Otherwise, check environment variable or default.
  final envUrl = String.fromEnvironment('MESHAGENT_API_URL', defaultValue: "");
  if (envUrl.isEmpty) {
    return 'https://api.meshagent.com';
  }
  return envUrl;
}