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/require-to-throw-message.md

@@ -0,0 +1,41 @@
+# Require a message for `toThrow()` (`require-to-throw-message`)
+
+<!-- end auto-generated rule header -->
+
+`toThrow()` (and its alias `toThrowError()`) is used to check if an error is
+thrown by a function call, such as in `expect(() => a()).toThrow()`. However, if
+no message is defined, then the test will pass for any thrown error. Requiring a
+message ensures that the intended error is thrown.
+
+## Rule details
+
+This rule triggers a warning if `toThrow()` or `toThrowError()` is used without
+an error message.
+
+The following patterns are considered warnings:
+
+```js
+test('all the things', async () => {
+  expect(() => a()).toThrow();
+
+  expect(() => a()).toThrowError();
+
+  await expect(a()).rejects.toThrow();
+
+  await expect(a()).rejects.toThrowError();
+});
+```
+
+The following patterns are not considered warnings:
+
+```js
+test('all the things', async () => {
+  expect(() => a()).toThrow('a');
+
+  expect(() => a()).toThrowError('a');
+
+  await expect(a()).rejects.toThrow('a');
+
+  await expect(a()).rejects.toThrowError('a');
+});
+```