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-plugin-import/docs/rules/no-namespace.md

@@ -0,0 +1,44 @@
+# import/no-namespace
+
+🔧 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
+
+<!-- end auto-generated rule header -->
+
+Enforce a convention of not using namespace (a.k.a. "wildcard" `*`) imports.
+
+The rule is auto-fixable when the namespace object is only used for direct member access, e.g. `namespace.a`.
+
+## Options
+
+This rule supports the following options:
+
+ - `ignore`: array of glob strings for modules that should be ignored by the rule.
+
+## Rule Details
+
+Valid:
+
+```js
+import defaultExport from './foo'
+import { a, b }  from './bar'
+import defaultExport, { a, b }  from './foobar'
+```
+
+```js
+/* eslint import/no-namespace: ["error", {ignore: ['*.ext']}] */
+import * as bar from './ignored-module.ext';
+```
+
+Invalid:
+
+```js
+import * as foo from 'foo';
+```
+
+```js
+import defaultExport, * as foo from 'foo';
+```
+
+## When Not To Use It
+
+If you want to use namespaces, you don't want to use this rule.