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/set-function-length/env.js

@@ -0,0 +1,25 @@
+'use strict';
+
+var gOPD = require('gopd');
+var bind = require('function-bind');
+
+var unbound = gOPD && gOPD(function () {}, 'length');
+// @ts-expect-error ts(2555) TS is overly strict with .call
+var bound = gOPD && gOPD(bind.call(function () {}), 'length');
+
+var functionsHaveConfigurableLengths = !!(unbound && unbound.configurable);
+
+var functionsHaveWritableLengths = !!(unbound && unbound.writable);
+
+var boundFnsHaveConfigurableLengths = !!(bound && bound.configurable);
+
+var boundFnsHaveWritableLengths = !!(bound && bound.writable);
+
+/** @type {import('./env')} */
+module.exports = {
+	__proto__: null,
+	boundFnsHaveConfigurableLengths: boundFnsHaveConfigurableLengths,
+	boundFnsHaveWritableLengths: boundFnsHaveWritableLengths,
+	functionsHaveConfigurableLengths: functionsHaveConfigurableLengths,
+	functionsHaveWritableLengths: functionsHaveWritableLengths
+};