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/icons/build/library/navigation.js

@@ -0,0 +1,20 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.default = void 0;
+var _react = require("react");
+var _primitives = require("@wordpress/primitives");
+/**
+ * WordPress dependencies
+ */
+
+const navigation = (0, _react.createElement)(_primitives.SVG, {
+  viewBox: "0 0 24 24",
+  xmlns: "http://www.w3.org/2000/svg"
+}, (0, _react.createElement)(_primitives.Path, {
+  d: "M12 4c-4.4 0-8 3.6-8 8s3.6 8 8 8 8-3.6 8-8-3.6-8-8-8zm0 14.5c-3.6 0-6.5-2.9-6.5-6.5S8.4 5.5 12 5.5s6.5 2.9 6.5 6.5-2.9 6.5-6.5 6.5zM9 16l4.5-3L15 8.4l-4.5 3L9 16z"
+}));
+var _default = exports.default = navigation;
+//# sourceMappingURL=navigation.js.map