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/@istanbuljs/schema/README.md

@@ -0,0 +1,42 @@
+# @istanbuljs/schema
+
+[![NPM Version][npm-image]][npm-url]
+[![NPM Downloads][downloads-image]][downloads-url]
+[![MIT][license-image]](LICENSE)
+
+Schemas describing various structures used by nyc and istanbuljs
+
+## Usage
+
+```js
+const {nyc} = require('@istanbuljs/schema').defaults;
+
+console.log(`Default exclude list:\n\t* ${nyc.exclude.join('\n\t* ')}`);
+```
+
+## Testing
+
+- **Runtime support**: See `engines.node` in `package.json` (currently `>=8`).
+- **Running tests**: Requires **Node.js >=22.3.0** (uses `node:test` snapshot testing via `t.assert.snapshot`).
+
+```bash
+npm test
+```
+
+To update snapshots:
+
+```bash
+npm run test:update-snapshots
+```
+
+## `@istanbuljs/schema` for enterprise
+
+Available as part of the Tidelift Subscription.
+
+The maintainers of `@istanbuljs/schema` and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source dependencies you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact dependencies you use. [Learn more.](https://tidelift.com/subscription/pkg/npm-istanbuljs-schema?utm_source=npm-istanbuljs-schema&utm_medium=referral&utm_campaign=enterprise)
+
+[npm-image]: https://img.shields.io/npm/v/@istanbuljs/schema.svg
+[npm-url]: https://npmjs.org/package/@istanbuljs/schema
+[downloads-image]: https://img.shields.io/npm/dm/@istanbuljs/schema.svg
+[downloads-url]: https://npmjs.org/package/@istanbuljs/schema
+[license-image]: https://img.shields.io/npm/l/@istanbuljs/schema.svg