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-empty-named-blocks.md

@@ -0,0 +1,49 @@
+# import/no-empty-named-blocks
+
+🔧💡 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix) and manually fixable by [editor suggestions](https://eslint.org/docs/latest/use/core-concepts#rule-suggestions).
+
+<!-- end auto-generated rule header -->
+
+Reports the use of empty named import blocks.
+
+## Rule Details
+
+### Valid
+
+```js
+import { mod } from 'mod'
+import Default, { mod } from 'mod'
+```
+
+When using typescript
+
+```js
+import type { mod } from 'mod'
+```
+
+When using flow
+
+```js
+import typeof { mod } from 'mod'
+```
+
+### Invalid
+
+```js
+import {} from 'mod'
+import Default, {} from 'mod'
+```
+
+When using typescript
+
+```js
+import type Default, {} from 'mod'
+import type {} from 'mod'
+```
+
+When using flow
+
+```js
+import typeof {} from 'mod'
+import typeof Default, {} from 'mod'
+```