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-default-export.md

@@ -0,0 +1,65 @@
+# import/no-default-export
+
+<!-- end auto-generated rule header -->
+
+Prohibit default exports. Mostly an inverse of [`prefer-default-export`].
+
+[`prefer-default-export`]: ./prefer-default-export.md
+
+## Rule Details
+
+The following patterns are considered warnings:
+
+```javascript
+// bad1.js
+
+// There is a default export.
+export const foo = 'foo';
+const bar = 'bar';
+export default 'bar';
+```
+
+```javascript
+// bad2.js
+
+// There is a default export.
+const foo = 'foo';
+export { foo as default }
+```
+
+The following patterns are not warnings:
+
+```javascript
+// good1.js
+
+// There is only a single module export and it's a named export.
+export const foo = 'foo';
+```
+
+```javascript
+// good2.js
+
+// There is more than one named export in the module.
+export const foo = 'foo';
+export const bar = 'bar';
+```
+
+```javascript
+// good3.js
+
+// There is more than one named export in the module
+const foo = 'foo';
+const bar = 'bar';
+export { foo, bar }
+```
+
+```javascript
+// export-star.js
+
+// Any batch export will disable this rule. The remote module is not inspected.
+export * from './other-module'
+```
+
+## When Not To Use It
+
+If you don't care if default imports are used, or if you prefer default imports over named imports.