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/_mapToArray.js

@@ -0,0 +1,18 @@
+/**
+ * Converts `map` to its key-value pairs.
+ *
+ * @private
+ * @param {Object} map The map to convert.
+ * @returns {Array} Returns the key-value pairs.
+ */
+function mapToArray(map) {
+  var index = -1,
+      result = Array(map.size);
+
+  map.forEach(function(value, key) {
+    result[++index] = [key, value];
+  });
+  return result;
+}
+
+module.exports = mapToArray;