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-hooks-on-top.md

@@ -0,0 +1,122 @@
+# Suggest having hooks before any test cases (`prefer-hooks-on-top`)
+
+<!-- end auto-generated rule header -->
+
+While hooks can be setup anywhere in a test file, they are always called in a
+specific order, which means it can be confusing if they're intermixed with test
+cases.
+
+This rule helps to ensure that hooks are always defined before test cases.
+
+## Rule details
+
+Examples of **incorrect** code for this rule
+
+```js
+/* eslint jest/prefer-hooks-on-top: "error" */
+
+describe('foo', () => {
+  beforeEach(() => {
+    seedMyDatabase();
+  });
+
+  it('accepts this input', () => {
+    // ...
+  });
+
+  beforeAll(() => {
+    createMyDatabase();
+  });
+
+  it('returns that value', () => {
+    // ...
+  });
+
+  describe('when the database has specific values', () => {
+    const specificValue = '...';
+
+    beforeEach(() => {
+      seedMyDatabase(specificValue);
+    });
+
+    it('accepts that input', () => {
+      // ...
+    });
+
+    it('throws an error', () => {
+      // ...
+    });
+
+    afterEach(() => {
+      clearLogger();
+    });
+    beforeEach(() => {
+      mockLogger();
+    });
+
+    it('logs a message', () => {
+      // ...
+    });
+  });
+
+  afterAll(() => {
+    removeMyDatabase();
+  });
+});
+```
+
+Examples of **correct** code for this rule
+
+```js
+/* eslint jest/prefer-hooks-on-top: "error" */
+
+describe('foo', () => {
+  beforeAll(() => {
+    createMyDatabase();
+  });
+
+  beforeEach(() => {
+    seedMyDatabase();
+  });
+
+  afterAll(() => {
+    clearMyDatabase();
+  });
+
+  it('accepts this input', () => {
+    // ...
+  });
+
+  it('returns that value', () => {
+    // ...
+  });
+
+  describe('when the database has specific values', () => {
+    const specificValue = '...';
+
+    beforeEach(() => {
+      seedMyDatabase(specificValue);
+    });
+
+    beforeEach(() => {
+      mockLogger();
+    });
+
+    afterEach(() => {
+      clearLogger();
+    });
+
+    it('accepts that input', () => {
+      // ...
+    });
+
+    it('throws an error', () => {
+      // ...
+    });
+
+    it('logs a message', () => {
+      // ...
+    });
+  });
+});
+```