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/container/ContainerExposedDependency.js

@@ -0,0 +1,66 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra, Zackary Jackson @ScriptedAlchemy, Marais Rossouw @maraisr
+*/
+
+"use strict";
+
+const ModuleDependency = require("../dependencies/ModuleDependency");
+const makeSerializable = require("../util/makeSerializable");
+
+/** @typedef {import("../serialization/ObjectMiddleware").ObjectDeserializerContext} ObjectDeserializerContext */
+/** @typedef {import("../serialization/ObjectMiddleware").ObjectSerializerContext} ObjectSerializerContext */
+
+class ContainerExposedDependency extends ModuleDependency {
+	/**
+	 * Creates an instance of ContainerExposedDependency.
+	 * @param {string} exposedName public name
+	 * @param {string} request request to module
+	 */
+	constructor(exposedName, request) {
+		super(request);
+		/** @type {string} */
+		this.exposedName = exposedName;
+	}
+
+	get type() {
+		return "container exposed";
+	}
+
+	get category() {
+		return "esm";
+	}
+
+	/**
+	 * Returns an identifier to merge equal requests.
+	 * @returns {string | null} an identifier to merge equal requests
+	 */
+	getResourceIdentifier() {
+		return `exposed dependency ${this.exposedName}=${this.request}`;
+	}
+
+	/**
+	 * Serializes this instance into the provided serializer context.
+	 * @param {ObjectSerializerContext} context context
+	 */
+	serialize(context) {
+		context.write(this.exposedName);
+		super.serialize(context);
+	}
+
+	/**
+	 * Restores this instance from the provided deserializer context.
+	 * @param {ObjectDeserializerContext} context context
+	 */
+	deserialize(context) {
+		this.exposedName = context.read();
+		super.deserialize(context);
+	}
+}
+
+makeSerializable(
+	ContainerExposedDependency,
+	"webpack/lib/container/ContainerExposedDependency"
+);
+
+module.exports = ContainerExposedDependency;