Fixes SoftOne customer creation when the literal C customer-code seed already exists by retrying without CODE so the tenant sequence can assign it.\n\nValidation:\n- php.exe -l softone-woocommerce-integration.php\n- php.exe -l includes/class-softone-woocommerce-integration.php\n- php.exe -l includes/class-softone-order-sync.php\n- php.exe -l includes/class-softone-customer-sync.php\n- php.exe -l tests/order-export-readiness-test.php\n- php.exe tests/order-export-readiness-test.php