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/webpack/lib/serialization/SetObjectSerializer.js

@@ -0,0 +1,42 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+*/
+
+"use strict";
+
+/** @typedef {import("./ObjectMiddleware").ObjectDeserializerContext} ObjectDeserializerContext */
+/** @typedef {import("./ObjectMiddleware").ObjectSerializerContext} ObjectSerializerContext */
+
+class SetObjectSerializer {
+	/**
+	 * Serializes this instance into the provided serializer context.
+	 * @template T
+	 * @param {Set<T>} obj set
+	 * @param {ObjectSerializerContext} context context
+	 */
+	serialize(obj, context) {
+		context.write(obj.size);
+		for (const value of obj) {
+			context.write(value);
+		}
+	}
+
+	/**
+	 * Restores this instance from the provided deserializer context.
+	 * @template T
+	 * @param {ObjectDeserializerContext} context context
+	 * @returns {Set<T>} date
+	 */
+	deserialize(context) {
+		/** @type {number} */
+		const size = context.read();
+		/** @type {Set<T>} */
+		const set = new Set();
+		for (let i = 0; i < size; i++) {
+			set.add(context.read());
+		}
+		return set;
+	}
+}
+
+module.exports = SetObjectSerializer;