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-import/docs/rules/no-internal-modules.md

@@ -0,0 +1,136 @@
+# import/no-internal-modules
+
+<!-- end auto-generated rule header -->
+
+Use this rule to prevent importing the submodules of other modules.
+
+## Rule Details
+
+This rule has two mutally exclusive options that are arrays of [minimatch/glob patterns](https://github.com/isaacs/node-glob#glob-primer) patterns:
+
+ - `allow` that include paths and import statements that can be imported with reaching.
+ - `forbid` that exclude paths and import statements that can be imported with reaching.
+
+### Examples
+
+Given the following folder structure:
+
+```pt
+my-project
+├── actions
+│   └── getUser.js
+│   └── updateUser.js
+├── reducer
+│   └── index.js
+│   └── user.js
+├── redux
+│   └── index.js
+│   └── configureStore.js
+└── app
+│   └── index.js
+│   └── settings.js
+└── entry.js
+```
+
+And the .eslintrc file:
+
+```json
+{
+  ...
+  "rules": {
+    "import/no-internal-modules": [ "error", {
+      "allow": [ "**/actions/*", "source-map-support/*" ],
+    } ]
+  }
+}
+```
+
+The following patterns are considered problems:
+
+```js
+/**
+ *  in my-project/entry.js
+ */
+
+import { settings } from './app/index'; // Reaching to "./app/index" is not allowed
+import userReducer from './reducer/user'; // Reaching to "./reducer/user" is not allowed
+import configureStore from './redux/configureStore'; // Reaching to "./redux/configureStore" is not allowed
+
+export { settings } from './app/index'; // Reaching to "./app/index" is not allowed
+export * from './reducer/user'; // Reaching to "./reducer/user" is not allowed
+```
+
+The following patterns are NOT considered problems:
+
+```js
+/**
+ *  in my-project/entry.js
+ */
+
+import 'source-map-support/register';
+import { settings } from '../app';
+import getUser from '../actions/getUser';
+
+export * from 'source-map-support/register';
+export { settings } from '../app';
+```
+
+Given the following folder structure:
+
+```pt
+my-project
+├── actions
+│   └── getUser.js
+│   └── updateUser.js
+├── reducer
+│   └── index.js
+│   └── user.js
+├── redux
+│   └── index.js
+│   └── configureStore.js
+└── app
+│   └── index.js
+│   └── settings.js
+└── entry.js
+```
+
+And the .eslintrc file:
+
+```json
+{
+  ...
+  "rules": {
+    "import/no-internal-modules": [ "error", {
+      "forbid": [ "**/actions/*", "source-map-support/*" ],
+    } ]
+  }
+}
+```
+
+The following patterns are considered problems:
+
+```js
+/**
+ *  in my-project/entry.js
+ */
+
+import 'source-map-support/register';
+import getUser from '../actions/getUser';
+
+export * from 'source-map-support/register';
+export getUser from '../actions/getUser';
+```
+
+The following patterns are NOT considered problems:
+
+```js
+/**
+ *  in my-project/entry.js
+ */
+
+import 'source-map-support';
+import { getUser } from '../actions';
+
+export * from 'source-map-support';
+export { getUser } from '../actions';
+```