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/_getNative.js

@@ -0,0 +1,17 @@
+var baseIsNative = require('./_baseIsNative'),
+    getValue = require('./_getValue');
+
+/**
+ * Gets the native function at `key` of `object`.
+ *
+ * @private
+ * @param {Object} object The object to query.
+ * @param {string} key The key of the method to get.
+ * @returns {*} Returns the function if it's native, else `undefined`.
+ */
+function getNative(object, key) {
+  var value = getValue(object, key);
+  return baseIsNative(value) ? value : undefined;
+}
+
+module.exports = getNative;