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/FalseIIFEUmdWarning.js

@@ -0,0 +1,20 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Arka Pratim Chaudhuri @arkapratimc
+*/
+
+"use strict";
+
+const WebpackError = require("./WebpackError");
+
+class FalseIIFEUmdWarning extends WebpackError {
+	constructor() {
+		super();
+		/** @type {string} */
+		this.name = "FalseIIFEUmdWarning";
+		this.message =
+			"Configuration:\nSetting 'output.iife' to 'false' is incompatible with 'output.library.type' set to 'umd'. This configuration may cause unexpected behavior, as UMD libraries are expected to use an IIFE (Immediately Invoked Function Expression) to support various module formats. Consider setting 'output.iife' to 'true' or choosing a different 'library.type' to ensure compatibility.\nLearn more: https://webpack.js.org/configuration/output/";
+	}
+}
+
+module.exports = FalseIIFEUmdWarning;