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-webpack-loader-syntax.md

@@ -0,0 +1,39 @@
+# import/no-webpack-loader-syntax
+
+<!-- end auto-generated rule header -->
+
+Forbid Webpack loader syntax in imports.
+
+[Webpack](https://webpack.js.org) allows specifying the [loaders](https://webpack.js.org/concepts/loaders/) to use in the import source string using a special syntax like this:
+
+```js
+var moduleWithOneLoader = require("my-loader!./my-awesome-module");
+```
+
+This syntax is non-standard, so it couples the code to Webpack. The recommended way to specify Webpack loader configuration is in a [Webpack configuration file](https://webpack.js.org/concepts/loaders/#configuration).
+
+## Rule Details
+
+### Fail
+
+```js
+import myModule from 'my-loader!my-module';
+import theme from 'style!css!./theme.css';
+
+var myModule = require('my-loader!./my-module');
+var theme = require('style!css!./theme.css');
+```
+
+### Pass
+
+```js
+import myModule from 'my-module';
+import theme from './theme.css';
+
+var myModule = require('my-module');
+var theme = require('./theme.css');
+```
+
+## When Not To Use It
+
+If you have a project that doesn't use Webpack you can safely disable this rule.