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/lodash/_copySymbols.js

@@ -0,0 +1,16 @@
+var copyObject = require('./_copyObject'),
+    getSymbols = require('./_getSymbols');
+
+/**
+ * Copies own symbols of `source` to `object`.
+ *
+ * @private
+ * @param {Object} source The object to copy symbols from.
+ * @param {Object} [object={}] The object to copy symbols to.
+ * @returns {Object} Returns `object`.
+ */
+function copySymbols(source, object) {
+  return copyObject(source, getSymbols(source), object);
+}
+
+module.exports = copySymbols;