prevent MySQL Workbench to add index for foreignkey constraint when it is first part of primary
That's currently a limitation of MySQL Workbench and has been mentioned recently already on Stackoverflow (can't find the question right now, sorry). MySQL Workbench doesn't use the special case where a foreign key uses columns that start the PK in that table. Please file a feature request at http://bugs.mysql.com if you think it would be worth implementing it.