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/exports-last.md

@@ -0,0 +1,51 @@
+# import/exports-last
+
+<!-- end auto-generated rule header -->
+
+This rule enforces that all exports are declared at the bottom of the file. This rule will report any export declarations that comes before any non-export statements.
+
+## This will be reported
+
+```JS
+
+const bool = true
+
+export default bool
+
+const str = 'foo'
+
+```
+
+```JS
+
+export const bool = true
+
+const str = 'foo'
+
+```
+
+## This will not be reported
+
+```JS
+const arr = ['bar']
+
+export const bool = true
+
+export default bool
+
+export function func() {
+  console.log('Hello World 🌍')
+}
+
+export const str = 'foo'
+```
+
+## When Not To Use It
+
+If you don't mind exports being sprinkled throughout a file, you may not want to enable this rule.
+
+### ES6 exports only
+
+The exports-last rule is currently only working on ES6 exports. You may not want to enable this rule if you're using CommonJS exports.
+
+If you need CommonJS support feel free to open an issue or create a PR.