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/is-docker/index.js

@@ -0,0 +1,29 @@
+'use strict';
+const fs = require('fs');
+
+let isDocker;
+
+function hasDockerEnv() {
+	try {
+		fs.statSync('/.dockerenv');
+		return true;
+	} catch (_) {
+		return false;
+	}
+}
+
+function hasDockerCGroup() {
+	try {
+		return fs.readFileSync('/proc/self/cgroup', 'utf8').includes('docker');
+	} catch (_) {
+		return false;
+	}
+}
+
+module.exports = () => {
+	if (isDocker === undefined) {
+		isDocker = hasDockerEnv() || hasDockerCGroup();
+	}
+
+	return isDocker;
+};