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/@wordpress/components/build/input-control/backdrop.js

@@ -0,0 +1,32 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.default = void 0;
+var _react = require("react");
+var _element = require("@wordpress/element");
+var _inputControlStyles = require("./styles/input-control-styles");
+/**
+ * WordPress dependencies
+ */
+
+/**
+ * Internal dependencies
+ */
+
+function Backdrop({
+  disabled = false,
+  isFocused = false
+}) {
+  return (0, _react.createElement)(_inputControlStyles.BackdropUI, {
+    "aria-hidden": "true",
+    className: "components-input-control__backdrop",
+    disabled: disabled,
+    isFocused: isFocused
+  });
+}
+const MemoizedBackdrop = (0, _element.memo)(Backdrop);
+var _default = MemoizedBackdrop;
+exports.default = _default;
+//# sourceMappingURL=backdrop.js.map