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/psl/vite.config.js

@@ -0,0 +1,20 @@
+import { resolve } from 'node:path';
+import { defineConfig } from 'vite';
+
+export default defineConfig({
+  build: {
+    target: 'es2015',
+    lib: {
+      entry: resolve(__dirname, 'index.js'),
+      name: 'psl',
+      formats: ['es', 'cjs', 'umd'],
+      fileName: format => (
+        format === 'umd'
+          ? 'psl.umd.cjs'
+          : format === 'cjs'
+            ? 'psl.cjs'
+            : 'psl.mjs'
+      ),
+    },
+  },
+});