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-focused-tests.md

@@ -0,0 +1,65 @@
+# Disallow focused tests (`no-focused-tests`)
+
+💼 This rule is enabled in the ✅ `recommended`
+[config](https://github.com/jest-community/eslint-plugin-jest/blob/main/README.md#shareable-configurations).
+
+💡 This rule is manually fixable by
+[editor suggestions](https://eslint.org/docs/developer-guide/working-with-rules#providing-suggestions).
+
+<!-- end auto-generated rule header -->
+
+<!-- prettier-ignore -->
+Jest has a feature that allows you to focus tests by appending `.only` or
+prepending `f` to a test-suite or a test-case. This feature is really helpful to
+debug a failing test, so you don’t have to execute all of your tests. After you
+have fixed your test and before committing the changes you have to remove
+`.only` to ensure all tests are executed on your build system.
+
+This rule reminds you to remove `.only` from your tests by raising a warning
+whenever you are using the exclusivity feature.
+
+## Rule details
+
+This rule looks for every `describe.only`, `it.only`, `test.only`, `fdescribe`,
+and `fit` occurrences within the source code. Of course there are some
+edge-cases which can’t be detected by this rule e.g.:
+
+```js
+const describeOnly = describe.only;
+describeOnly.apply(describe);
+```
+
+The following patterns are considered warnings:
+
+```js
+describe.only('foo', () => {});
+it.only('foo', () => {});
+describe['only']('bar', () => {});
+it['only']('bar', () => {});
+test.only('foo', () => {});
+test['only']('bar', () => {});
+fdescribe('foo', () => {});
+fit('foo', () => {});
+fit.each`
+  table
+`();
+```
+
+These patterns would not be considered warnings:
+
+```js
+describe('foo', () => {});
+it('foo', () => {});
+describe.skip('bar', () => {});
+it.skip('bar', () => {});
+test('foo', () => {});
+test.skip('bar', () => {});
+it.each()();
+it.each`
+  table
+`();
+test.each()();
+test.each`
+  table
+`();
+```