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/resolve/test/dotdot.js

@@ -0,0 +1,29 @@
+var path = require('path');
+var test = require('tape');
+var resolve = require('../');
+
+test('dotdot', function (t) {
+    t.plan(4);
+    var dir = path.join(__dirname, '/dotdot/abc');
+
+    resolve('..', { basedir: dir }, function (err, res, pkg) {
+        t.ifError(err);
+        t.equal(res, path.join(__dirname, 'dotdot/index.js'));
+    });
+
+    resolve('.', { basedir: dir }, function (err, res, pkg) {
+        t.ifError(err);
+        t.equal(res, path.join(dir, 'index.js'));
+    });
+});
+
+test('dotdot sync', function (t) {
+    t.plan(2);
+    var dir = path.join(__dirname, '/dotdot/abc');
+
+    var a = resolve.sync('..', { basedir: dir });
+    t.equal(a, path.join(__dirname, 'dotdot/index.js'));
+
+    var b = resolve.sync('.', { basedir: dir });
+    t.equal(b, path.join(dir, 'index.js'));
+});