Refactor EDAC_KEY_VALID condition for clarity

Group the defined() and value checks with parentheses so the intent reads
as a single "license key is not valid" unit, per code review suggestion.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: SteveJonesDev

includes/classes/class-admin-toolbar.php

@@ -108,7 +108,7 @@ private function get_default_menu_items(): array {
 		];
 
 		// Add Get Pro submenu item (only show if pro is not installed or license is not valid).
-		if ( ! defined( 'EDACP_VERSION' ) || ! defined( 'EDAC_KEY_VALID' ) || ! EDAC_KEY_VALID ) {
+		if ( ! defined( 'EDACP_VERSION' ) || ! ( defined( 'EDAC_KEY_VALID' ) && EDAC_KEY_VALID ) ) {
 			$pro_link = function_exists( 'edac_generate_link_type' ) 
 				? edac_generate_link_type( [ 'utm_content' => 'admin-toolbar' ] )
 				: 'https://equalizedigital.com/accessibility-checker/pricing/';