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/axios/lib/helpers/deprecatedMethod.js

@@ -0,0 +1,31 @@
+'use strict';
+
+/*eslint no-console:0*/
+
+/**
+ * Supply a warning to the developer that a method they are using
+ * has been deprecated.
+ *
+ * @param {string} method The name of the deprecated method
+ * @param {string} [instead] The alternate method to use if applicable
+ * @param {string} [docs] The documentation URL to get further details
+ *
+ * @returns {void}
+ */
+export default function deprecatedMethod(method, instead, docs) {
+  try {
+    console.warn(
+      'DEPRECATED method `' +
+        method +
+        '`.' +
+        (instead ? ' Use `' + instead + '` instead.' : '') +
+        ' This method will be removed in a future release.'
+    );
+
+    if (docs) {
+      console.warn('For more information about usage see ' + docs);
+    }
+  } catch (e) {
+    /* Ignore */
+  }
+}