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/getRangePairs.js

@@ -0,0 +1,28 @@
+'use strict';
+
+var test = require('tape');
+var forEach = require('for-each');
+var semver = require('semver');
+
+var getRangePairs = require('../getRangePairs');
+var getConditionsForCategory = require('../getConditionsForCategory');
+
+test('getRangePairs', function (t) {
+	var pairs = getRangePairs();
+	t.ok(Array.isArray(pairs), 'returns an array');
+
+	forEach(pairs, function (entry, i) {
+		t.ok(Array.isArray(entry), 'entry ' + i + ' is an array');
+
+		var range = entry[0];
+		var category = entry[1];
+
+		t.ok(semver.validRange(range), i + ': item 0 is a valid semver range');
+		t.doesNotThrow(
+			function () { getConditionsForCategory(category); },
+			i + ': item 1 is a valid category'
+		);
+	});
+
+	t.end();
+});