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/data-uri-to-buffer/dist/node.d.ts

@@ -0,0 +1,8 @@
+export type { ParsedDataURI } from './common';
+/**
+ * Returns a `Buffer` instance from the given data URI `uri`.
+ *
+ * @param {String} uri Data URI to turn into a Buffer instance
+ */
+export declare const dataUriToBuffer: (uri: string | URL) => import("./common").ParsedDataURI;
+//# sourceMappingURL=node.d.ts.map