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-equality-matcher.md

@@ -0,0 +1,34 @@
+# Suggest using the built-in equality matchers (`prefer-equality-matcher`)
+
+💡 This rule is manually fixable by
+[editor suggestions](https://eslint.org/docs/developer-guide/working-with-rules#providing-suggestions).
+
+<!-- end auto-generated rule header -->
+
+Jest has built-in matchers for expecting equality, which allow for more readable
+tests and error messages if an expectation fails.
+
+## Rule details
+
+This rule checks for _strict_ equality checks (`===` & `!==`) in tests that
+could be replaced with one of the following built-in equality matchers:
+
+- `toBe`
+- `toEqual`
+- `toStrictEqual`
+
+Examples of **incorrect** code for this rule:
+
+```js
+expect(x === 5).toBe(true);
+expect(name === 'Carl').not.toEqual(true);
+expect(myObj !== thatObj).toStrictEqual(true);
+```
+
+Examples of **correct** code for this rule:
+
+```js
+expect(x).toBe(5);
+expect(name).not.toEqual('Carl');
+expect(myObj).toStrictEqual(thatObj);
+```