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/newline-after-import.md

@@ -0,0 +1,167 @@
+# import/newline-after-import
+
+🔧 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
+
+<!-- end auto-generated rule header -->
+
+Enforces having one or more empty lines after the last top-level import statement or require call.
+
+## Rule Details
+
+This rule supports the following options:
+
+ - `count` which sets the number of newlines that are enforced after the last top-level import statement or require call. This option defaults to `1`.
+
+ - `exactCount` which enforce the exact numbers of newlines that is mentioned in `count`. This option defaults to `false`.
+
+ - `considerComments` which enforces the rule on comments after the last import-statement as well when set to true. This option defaults to `false`.
+
+Valid:
+
+```js
+import defaultExport from './foo';
+
+const FOO = 'BAR';
+```
+
+```js
+import defaultExport from './foo';
+import { bar }  from 'bar-lib';
+
+const FOO = 'BAR';
+```
+
+```js
+const FOO = require('./foo');
+const BAR = require('./bar');
+
+const BAZ = 1;
+```
+
+Invalid:
+
+```js
+import * as foo from 'foo'
+const FOO = 'BAR';
+```
+
+```js
+import * as foo from 'foo';
+const FOO = 'BAR';
+
+import { bar }  from 'bar-lib';
+```
+
+```js
+const FOO = require('./foo');
+const BAZ = 1;
+const BAR = require('./bar');
+```
+
+With `count` set to `2` this will be considered valid:
+
+```js
+import defaultExport from './foo';
+
+
+const FOO = 'BAR';
+```
+
+```js
+import defaultExport from './foo';
+
+
+
+const FOO = 'BAR';
+```
+
+With `count` set to `2` these will be considered invalid:
+
+```js
+import defaultExport from './foo';
+const FOO = 'BAR';
+```
+
+```js
+import defaultExport from './foo';
+
+const FOO = 'BAR';
+```
+
+With `count` set to `2` and `exactCount` set to `true` this will be considered valid:
+
+```js
+import defaultExport from './foo';
+
+
+const FOO = 'BAR';
+```
+
+With `count` set to `2` and `exactCount` set to `true` these will be considered invalid:
+
+```js
+import defaultExport from './foo';
+const FOO = 'BAR';
+```
+
+```js
+import defaultExport from './foo';
+
+const FOO = 'BAR';
+```
+
+```js
+import defaultExport from './foo';
+
+
+
+const FOO = 'BAR';
+```
+
+```js
+import defaultExport from './foo';
+
+
+
+
+const FOO = 'BAR';
+```
+
+With `considerComments` set to `false` this will be considered valid:
+
+```js
+import defaultExport from './foo'
+// some comment here.
+const FOO = 'BAR'
+```
+
+With `considerComments` set to `true` this will be considered valid:
+
+```js
+import defaultExport from './foo'
+
+// some comment here.
+const FOO = 'BAR'
+```
+
+With `considerComments` set to `true` this will be considered invalid:
+
+```js
+import defaultExport from './foo'
+// some comment here.
+const FOO = 'BAR'
+```
+
+## Example options usage
+
+```json
+{
+  "rules": {
+    "import/newline-after-import": ["error", { "count": 2 }]
+  }
+}
+```
+
+## When Not To Use It
+
+If you like to visually group module imports with its usage, you don't want to use this rule.