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-what/lib/commonjs/parse.d.ts

@@ -0,0 +1,20 @@
+import { Selector, Traversal } from "./types";
+/**
+ * Checks whether a specific selector is a traversal.
+ * This is useful eg. in swapping the order of elements that
+ * are not traversals.
+ *
+ * @param selector Selector to check.
+ */
+export declare function isTraversal(selector: Selector): selector is Traversal;
+/**
+ * Parses `selector`, optionally with the passed `options`.
+ *
+ * @param selector Selector to parse.
+ * @param options Options for parsing.
+ * @returns Returns a two-dimensional array.
+ * The first dimension represents selectors separated by commas (eg. `sub1, sub2`),
+ * the second contains the relevant tokens for that selector.
+ */
+export declare function parse(selector: string): Selector[][];
+//# sourceMappingURL=parse.d.ts.map