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/yargs/build/lib/utils/maybe-async-result.js

@@ -0,0 +1,17 @@
+import { isPromise } from './is-promise.js';
+export function maybeAsyncResult(getResult, resultHandler, errorHandler = (err) => {
+    throw err;
+}) {
+    try {
+        const result = isFunction(getResult) ? getResult() : getResult;
+        return isPromise(result)
+            ? result.then((result) => resultHandler(result))
+            : resultHandler(result);
+    }
+    catch (err) {
+        return errorHandler(err);
+    }
+}
+function isFunction(arg) {
+    return typeof arg === 'function';
+}