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/eslint/lib/rules/no-async-promise-executor.js

@@ -0,0 +1,39 @@
+/**
+ * @fileoverview disallow using an async function as a Promise executor
+ * @author Teddy Katz
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+/** @type {import('../shared/types').Rule} */
+module.exports = {
+    meta: {
+        type: "problem",
+
+        docs: {
+            description: "Disallow using an async function as a Promise executor",
+            recommended: true,
+            url: "https://eslint.org/docs/latest/rules/no-async-promise-executor"
+        },
+
+        fixable: null,
+        schema: [],
+        messages: {
+            async: "Promise executor functions should not be async."
+        }
+    },
+
+    create(context) {
+        return {
+            "NewExpression[callee.name='Promise'][arguments.0.async=true]"(node) {
+                context.report({
+                    node: context.sourceCode.getFirstToken(node.arguments[0], token => token.value === "async"),
+                    messageId: "async"
+                });
+            }
+        };
+    }
+};