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/resolve/lib/normalize-options.js

@@ -0,0 +1,10 @@
+module.exports = function (x, opts) {
+    /**
+     * This file is purposefully a passthrough. It's expected that third-party
+     * environments will override it at runtime in order to inject special logic
+     * into `resolve` (by manipulating the options). One such example is the PnP
+     * code path in Yarn.
+     */
+
+    return opts || {};
+};