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/webpack-merge/dist/utils.d.ts

@@ -0,0 +1,17 @@
+declare function isRegex(o: any): boolean;
+declare function isFunction(functionToCheck: any): any;
+declare function isPlainObject(a: any): boolean;
+declare function isUndefined(a: any): boolean;
+/**
+ * According to Webpack docs, a "test" should be the following:
+ *
+ * - A string
+ * - A RegExp
+ * - A function
+ * - An array of conditions (may be nested)
+ * - An object of conditions (may be nested)
+ *
+ * https://webpack.js.org/configuration/module/#condition
+ */
+declare function isSameCondition(a: any, b: any): boolean;
+export { isRegex, isFunction, isPlainObject, isUndefined, isSameCondition };