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/messages/eslintrc-plugins.js

@@ -0,0 +1,24 @@
+"use strict";
+
+module.exports = function({ plugins }) {
+
+    const isArrayOfStrings = typeof plugins[0] === "string";
+
+    return `
+A config object has a "plugins" key defined as an array${isArrayOfStrings ? " of strings" : ""}.
+
+Flat config requires "plugins" to be an object in this form:
+
+    {
+        plugins: {
+            ${isArrayOfStrings && plugins[0] ? plugins[0] : "namespace"}: pluginObject
+        }
+    }
+
+Please see the following page for information on how to convert your config object into the correct format:
+https://eslint.org/docs/latest/use/configure/migration-guide#importing-plugins-and-custom-parsers
+
+If you're using a shareable config that you cannot rewrite in flat config format, then use the compatibility utility:
+https://eslint.org/docs/latest/use/configure/migration-guide#using-eslintrc-configs-in-flat-config
+`;
+};