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/previous.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 previous = (0, _react.createElement)(_primitives.SVG, {
+  xmlns: "http://www.w3.org/2000/svg",
+  viewBox: "0 0 24 24"
+}, (0, _react.createElement)(_primitives.Path, {
+  d: "M11.6 7l-1.1-1L5 12l5.5 6 1.1-1L7 12l4.6-5zm6 0l-1.1-1-5.5 6 5.5 6 1.1-1-4.6-5 4.6-5z"
+}));
+var _default = exports.default = previous;
+//# sourceMappingURL=previous.js.map