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/node-exports-info/test/getRange.js

@@ -0,0 +1,26 @@
+'use strict';
+
+var test = require('tape');
+var forEach = require('for-each');
+
+var getRange = require('../getRange');
+var getRangePairs = require('../getRangePairs');
+
+test('getRange', function (t) {
+	t['throws'](
+		// @ts-expect-error
+		function () { getRange('not a category'); },
+		RangeError,
+		'invalid category throws'
+	);
+
+	forEach(getRangePairs(), function (entry) {
+		var range = entry[0];
+		var category = entry[1];
+
+		var actualRange = getRange(category);
+		t.equal(actualRange, range, 'yielded range for ' + category + ' is as expected');
+	});
+
+	t.end();
+});