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/define-data-property/index.d.ts

@@ -0,0 +1,12 @@
+
+declare function defineDataProperty(
+    obj: Record<PropertyKey, unknown>,
+    property: keyof typeof obj,
+    value: typeof obj[typeof property],
+    nonEnumerable?: boolean | null,
+    nonWritable?: boolean | null,
+    nonConfigurable?: boolean | null,
+    loose?: boolean
+): void;
+
+export = defineDataProperty;