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-strict-equal.md

@@ -0,0 +1,27 @@
+# Suggest using `toStrictEqual()` (`prefer-strict-equal`)
+
+💡 This rule is manually fixable by
+[editor suggestions](https://eslint.org/docs/developer-guide/working-with-rules#providing-suggestions).
+
+<!-- end auto-generated rule header -->
+
+`toStrictEqual` not only checks that two objects contain the same data but also
+that they have the same structure. It is common to expect objects to not only
+have identical values but also to have identical keys. A stricter equality will
+catch cases where two objects do not have identical keys.
+
+## Rule details
+
+This rule triggers a warning if `toEqual()` is used to assert equality.
+
+The following pattern is considered warning:
+
+```js
+expect({ a: 'a', b: undefined }).toEqual({ a: 'a' }); // true
+```
+
+The following pattern is not warning:
+
+```js
+expect({ a: 'a', b: undefined }).toStrictEqual({ a: 'a' }); // false
+```