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/prefer-mock-promise-shorthand.md

@@ -0,0 +1,39 @@
+# Prefer mock resolved/rejected shorthands for promises (`prefer-mock-promise-shorthand`)
+
+🔧 This rule is automatically fixable by the
+[`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
+
+<!-- end auto-generated rule header -->
+
+When working with mocks of functions that return promises, Jest provides some
+API sugar functions to reduce the amount of boilerplate you have to write.
+
+These methods should be preferred when possible.
+
+## Rule details
+
+The following patterns are warnings:
+
+```js
+jest.fn().mockImplementation(() => Promise.resolve(123));
+jest
+  .spyOn(fs.promises, 'readFile')
+  .mockReturnValue(Promise.reject(new Error('oh noes!')));
+
+myFunction
+  .mockReturnValueOnce(Promise.resolve(42))
+  .mockImplementationOnce(() => Promise.resolve(42))
+  .mockReturnValue(Promise.reject(new Error('too many calls!')));
+```
+
+The following patterns are not warnings:
+
+```js
+jest.fn().mockResolvedValue(123);
+jest.spyOn(fs.promises, 'readFile').mockRejectedValue(new Error('oh noes!'));
+
+myFunction
+  .mockResolvedValueOnce(42)
+  .mockResolvedValueOnce(42)
+  .mockRejectedValue(new Error('too many calls!'));
+```