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/toidentifier/index.js

@@ -0,0 +1,32 @@
+/*!
+ * toidentifier
+ * Copyright(c) 2016 Douglas Christopher Wilson
+ * MIT Licensed
+ */
+
+'use strict'
+
+/**
+ * Module exports.
+ * @public
+ */
+
+module.exports = toIdentifier
+
+/**
+ * Trasform the given string into a JavaScript identifier
+ *
+ * @param {string} str
+ * @returns {string}
+ * @public
+ */
+
+function toIdentifier (str) {
+  return str
+    .split(' ')
+    .map(function (token) {
+      return token.slice(0, 1).toUpperCase() + token.slice(1)
+    })
+    .join('')
+    .replace(/[^ _0-9a-z]/gi, '')
+}