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/webpack-dev-middleware/dist/utils/ready.js

@@ -0,0 +1,26 @@
+"use strict";
+
+/** @typedef {import("../index.js").IncomingMessage} IncomingMessage */
+
+/** @typedef {import("../index.js").ServerResponse} ServerResponse */
+
+/**
+ * @template {IncomingMessage} Request
+ * @template {ServerResponse} Response
+ * @param {import("../index.js").Context<Request, Response>} context
+ * @param {(...args: any[]) => any} callback
+ * @param {Request} [req]
+ * @returns {void}
+ */
+function ready(context, callback, req) {
+  if (context.state) {
+    callback(context.stats);
+    return;
+  }
+
+  const name = req && req.url || callback.name;
+  context.logger.info(`wait until bundle finished${name ? `: ${name}` : ""}`);
+  context.callbacks.push(callback);
+}
+
+module.exports = ready;