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-jest/docs/rules/no-export.md

@@ -0,0 +1,50 @@
+# Disallow using `exports` in files containing tests (`no-export`)
+
+💼 This rule is enabled in the ✅ `recommended`
+[config](https://github.com/jest-community/eslint-plugin-jest/blob/main/README.md#shareable-configurations).
+
+<!-- end auto-generated rule header -->
+
+Prevents using `exports` if a file has one or more tests in it.
+
+## Rule details
+
+This rule aims to eliminate duplicate runs of tests by exporting things from
+test files. If you import from a test file, then all the tests in that file will
+be run in each imported instance, so bottom line, don't export from a test, but
+instead move helper functions into a separate file when they need to be shared
+across tests.
+
+Examples of **incorrect** code for this rule:
+
+```js
+export function myHelper() {}
+
+module.exports = function () {};
+
+module.exports = {
+  something: 'that should be moved to a non-test file',
+};
+
+describe('a test', () => {
+  expect(1).toBe(1);
+});
+```
+
+Examples of **correct** code for this rule:
+
+```js
+function myHelper() {}
+
+const myThing = {
+  something: 'that can live here',
+};
+
+describe('a test', () => {
+  expect(1).toBe(1);
+});
+```
+
+## When Not To Use It
+
+Don't use this rule on non-jest test files.