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/ModuleWarning.js

@@ -0,0 +1,71 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+
+"use strict";
+
+const { cleanUp } = require("./ErrorHelpers");
+const WebpackError = require("./WebpackError");
+const makeSerializable = require("./util/makeSerializable");
+
+/** @typedef {import("./serialization/ObjectMiddleware").ObjectDeserializerContext} ObjectDeserializerContext */
+/** @typedef {import("./serialization/ObjectMiddleware").ObjectSerializerContext} ObjectSerializerContext */
+
+class ModuleWarning extends WebpackError {
+	/**
+	 * Creates an instance of ModuleWarning.
+	 * @param {Error} warning error thrown
+	 * @param {{ from?: string | null }} info additional info
+	 */
+	constructor(warning, { from = null } = {}) {
+		let message = "Module Warning";
+
+		message += from ? ` (from ${from}):\n` : ": ";
+
+		if (warning && typeof warning === "object" && warning.message) {
+			message += warning.message;
+		} else if (warning) {
+			message += String(warning);
+		}
+
+		super(message);
+
+		/** @type {string} */
+		this.name = "ModuleWarning";
+		this.warning = warning;
+		this.details =
+			warning && typeof warning === "object" && warning.stack
+				? cleanUp(warning.stack, this.message)
+				: undefined;
+	}
+
+	/**
+	 * Serializes this instance into the provided serializer context.
+	 * @param {ObjectSerializerContext} context context
+	 */
+	serialize(context) {
+		const { write } = context;
+
+		write(this.warning);
+
+		super.serialize(context);
+	}
+
+	/**
+	 * Restores this instance from the provided deserializer context.
+	 * @param {ObjectDeserializerContext} context context
+	 */
+	deserialize(context) {
+		const { read } = context;
+
+		this.warning = read();
+
+		super.deserialize(context);
+	}
+}
+
+makeSerializable(ModuleWarning, "webpack/lib/ModuleWarning");
+
+/** @type {typeof ModuleWarning} */
+module.exports = ModuleWarning;