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-duplicate-hooks.md

@@ -0,0 +1,77 @@
+# Disallow duplicate setup and teardown hooks (`no-duplicate-hooks`)
+
+<!-- end auto-generated rule header -->
+
+A `describe` block should not contain duplicate hooks.
+
+## Rule details
+
+Examples of **incorrect** code for this rule
+
+```js
+/* eslint jest/no-duplicate-hooks: "error" */
+
+describe('foo', () => {
+  beforeEach(() => {
+    // some setup
+  });
+  beforeEach(() => {
+    // some setup
+  });
+  test('foo_test', () => {
+    // some test
+  });
+});
+
+// Nested describe scenario
+describe('foo', () => {
+  beforeEach(() => {
+    // some setup
+  });
+  test('foo_test', () => {
+    // some test
+  });
+  describe('bar', () => {
+    test('bar_test', () => {
+      afterAll(() => {
+        // some teardown
+      });
+      afterAll(() => {
+        // some teardown
+      });
+    });
+  });
+});
+```
+
+Examples of **correct** code for this rule
+
+```js
+/* eslint jest/no-duplicate-hooks: "error" */
+
+describe('foo', () => {
+  beforeEach(() => {
+    // some setup
+  });
+  test('foo_test', () => {
+    // some test
+  });
+});
+
+// Nested describe scenario
+describe('foo', () => {
+  beforeEach(() => {
+    // some setup
+  });
+  test('foo_test', () => {
+    // some test
+  });
+  describe('bar', () => {
+    test('bar_test', () => {
+      beforeEach(() => {
+        // some setup
+      });
+    });
+  });
+});
+```