Improve error message to include specific missing command

Co-authored-by: swissspidy <841956+swissspidy@users.noreply.github.com>

Author: Copilot

features/scaffold-package-readme.feature

@@ -313,7 +313,7 @@ Feature: Scaffold a README.md file for an existing package
     When I try `wp scaffold package-readme foo`
     Then STDERR should be:
       """
-      Error: Missing one or more commands defined in composer.json -> extra -> commands.
+      Error: Command 'profile' is not registered. Make sure it is loaded before running package-readme.
       """
     And the return code should be 1
 

src/ScaffoldPackageCommand.php

@@ -333,7 +333,7 @@ public function package_readme( $args, $assoc_args ) {
 				} while ( $parent_command && $bits );
 
 				if ( empty( $parent_command ) ) {
-					WP_CLI::error( 'Missing one or more commands defined in composer.json -> extra -> commands.' );
+					WP_CLI::error( "Command '{$command}' is not registered. Make sure it is loaded before running package-readme." );
 				}
 
 				$longdesc = isset( $parent_command['longdesc'] ) ? $parent_command['longdesc'] : '';