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/css-tree/lib/convertor/create.js

@@ -0,0 +1,28 @@
+import { List } from '../utils/List.js';
+
+export function createConvertor(walk) {
+    return {
+        fromPlainObject(ast) {
+            walk(ast, {
+                enter(node) {
+                    if (node.children && node.children instanceof List === false) {
+                        node.children = new List().fromArray(node.children);
+                    }
+                }
+            });
+
+            return ast;
+        },
+        toPlainObject(ast) {
+            walk(ast, {
+                leave(node) {
+                    if (node.children && node.children instanceof List) {
+                        node.children = node.children.toArray();
+                    }
+                }
+            });
+
+            return ast;
+        }
+    };
+};

node_modules/css-tree/lib/convertor/index.js

@@ -0,0 +1,4 @@
+import { createConvertor } from './create.js';
+import walker from '../walker/index.js';
+
+export default createConvertor(walker);