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/SizeFormatHelpers.js

@@ -0,0 +1,26 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Sean Larkin @thelarkinn
+*/
+
+"use strict";
+
+/**
+ * Returns the formatted size.
+ * @param {number=} size the size in bytes
+ * @returns {string} the formatted size
+ */
+module.exports.formatSize = (size) => {
+	if (typeof size !== "number" || Number.isNaN(size) === true) {
+		return "unknown size";
+	}
+
+	if (size <= 0) {
+		return "0 bytes";
+	}
+
+	const abbreviations = ["bytes", "KiB", "MiB", "GiB"];
+	const index = Math.floor(Math.log(size) / Math.log(1024));
+
+	return `${Number((size / 1024 ** index).toPrecision(3))} ${abbreviations[index]}`;
+};