fix: prevent asset conflicts between React and Grid.js versions

Add coexistence checks to all enqueue methods to prevent loading
both React and Grid.js assets simultaneously.

Changes:
- ReactAdmin.php: Only enqueue React assets when ?react=1
- Init.php: Skip Grid.js when React active on admin pages
- Form.php, Coupon.php, Access.php: Restore classic assets when ?react=0
- Customer.php, Product.php, License.php: Add coexistence checks

Now the toggle between Classic and React versions works correctly.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

node_modules/@wordpress/scripts/utils/block-json.js

@@ -0,0 +1,41 @@
+const moduleFields = new Set( [ 'viewScriptModule', 'viewModule' ] );
+const scriptFields = new Set( [ 'viewScript', 'script', 'editorScript' ] );
+
+/**
+ * @param {Object} blockJson
+ * @return {null|Record<string, unknown>} Fields
+ */
+function getBlockJsonModuleFields( blockJson ) {
+	let result = null;
+	for ( const field of moduleFields ) {
+		if ( Object.hasOwn( blockJson, field ) ) {
+			if ( ! result ) {
+				result = {};
+			}
+			result[ field ] = blockJson[ field ];
+		}
+	}
+	return result;
+}
+
+/**
+ * @param {Object} blockJson
+ * @return {null|Record<string, unknown>} Fields
+ */
+function getBlockJsonScriptFields( blockJson ) {
+	let result = null;
+	for ( const field of scriptFields ) {
+		if ( Object.hasOwn( blockJson, field ) ) {
+			if ( ! result ) {
+				result = {};
+			}
+			result[ field ] = blockJson[ field ];
+		}
+	}
+	return result;
+}
+
+module.exports = {
+	getBlockJsonModuleFields,
+	getBlockJsonScriptFields,
+};