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-named-default.md

@@ -0,0 +1,36 @@
+# import/no-named-default
+
+<!-- end auto-generated rule header -->
+
+Reports use of a default export as a locally named import.
+
+Rationale: the syntax exists to import default exports expressively, let's use it.
+
+Note that type imports, as used by [Flow], are always ignored.
+
+[Flow]: https://flow.org/
+
+## Rule Details
+
+Given:
+
+```js
+// foo.js
+export default 'foo';
+export const bar = 'baz';
+```
+
+...these would be valid:
+
+```js
+import foo from './foo.js';
+import foo, { bar } from './foo.js';
+```
+
+...and these would be reported:
+
+```js
+// message: Using exported name 'bar' as identifier for default export.
+import { default as foo } from './foo.js';
+import { default as foo, bar } from './foo.js';
+```