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-mutable-exports.md

@@ -0,0 +1,54 @@
+# import/no-mutable-exports
+
+<!-- end auto-generated rule header -->
+
+Forbids the use of mutable exports with `var` or `let`.
+
+## Rule Details
+
+Valid:
+
+```js
+export const count = 1
+export function getCount() {}
+export class Counter {}
+```
+
+...whereas here exports will be reported:
+
+```js
+export let count = 2
+export var count = 3
+
+let count = 4
+export { count } // reported here
+```
+
+## Functions/Classes
+
+Note that exported function/class declaration identifiers may be reassigned,
+but are not flagged by this rule at this time. They may be in the future, if a
+reassignment is detected, i.e.
+
+```js
+// possible future behavior!
+export class Counter {} // reported here: exported class is reassigned on line [x].
+Counter = KitchenSink // not reported here unless you enable no-class-assign
+
+// this pre-declaration reassignment is valid on account of function hoisting
+getCount = function getDuke() {} // not reported here without no-func-assign
+export function getCount() {} // reported here: exported function is reassigned on line [x].
+```
+
+To prevent general reassignment of these identifiers, exported or not, you may
+want to enable the following core ESLint rules:
+
+ - [no-func-assign]
+ - [no-class-assign]
+
+[no-func-assign]: https://eslint.org/docs/rules/no-func-assign
+[no-class-assign]: https://eslint.org/docs/rules/no-class-assign
+
+## When Not To Use It
+
+If your environment correctly implements mutable export bindings.