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/fs-monkey/docs/api/patchFs.md

@@ -0,0 +1,40 @@
+# `patchFs(vol[, fs])`
+
+Rewrites Node's filesystem module `fs` with *fs-like* object.
+
+ - `vol` - fs-like object
+ - `fs` *(optional)* - a filesystem to patch, defaults to `require('fs')`
+
+```js
+import {patchFs} from 'fs-monkey';
+
+const myfs = {
+    readFileSync: () => 'hello world',
+};
+
+patchFs(myfs);
+console.log(require('fs').readFileSync('/foo/bar')); // hello world
+```
+
+You don't need to create *fs-like* objects yourself, use [`memfs`](https://github.com/streamich/memfs)
+to create a virtual filesystem for you:
+
+```js
+import {vol} from 'memfs';
+import {patchFs} from 'fs-monkey';
+
+vol.fromJSON({'/dir/foo': 'bar'});
+patchFs(vol);
+console.log(require('fs').readdirSync('/')); // [ 'dir' ]
+```
+
+Promises API is supported as well:
+
+```js
+import {vol} from 'memfs';
+import {patchFs} from 'fs-monkey';
+
+vol.fromJSON({'/dir/foo': 'bar'});
+patchFs(vol);
+require('fs').promises.readFile('/dir/foo', 'UTF-8').then(console.log); // bar
+```