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-server/client/overlay/runtime-error.js

@@ -0,0 +1,47 @@
+/**
+ *
+ * @param {Error} error
+ */
+function parseErrorToStacks(error) {
+  if (!error || !(error instanceof Error)) {
+    throw new Error("parseErrorToStacks expects Error object");
+  }
+  if (typeof error.stack === "string") {
+    return error.stack.split("\n").filter(function (stack) {
+      return stack !== "Error: ".concat(error.message);
+    });
+  }
+}
+
+/**
+ * @callback ErrorCallback
+ * @param {ErrorEvent} error
+ * @returns {void}
+ */
+
+/**
+ * @param {ErrorCallback} callback
+ */
+function listenToRuntimeError(callback) {
+  window.addEventListener("error", callback);
+  return function cleanup() {
+    window.removeEventListener("error", callback);
+  };
+}
+
+/**
+ * @callback UnhandledRejectionCallback
+ * @param {PromiseRejectionEvent} rejectionEvent
+ * @returns {void}
+ */
+
+/**
+ * @param {UnhandledRejectionCallback} callback
+ */
+function listenToUnhandledRejection(callback) {
+  window.addEventListener("unhandledrejection", callback);
+  return function cleanup() {
+    window.removeEventListener("unhandledrejection", callback);
+  };
+}
+export { listenToRuntimeError, listenToUnhandledRejection, parseErrorToStacks };