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/unbox-primitive/index.d.ts

@@ -0,0 +1,13 @@
+declare function unboxPrimitive<T extends unboxPrimitive.Boxed>(value: T): unboxPrimitive.Unbox<T>;
+
+declare namespace unboxPrimitive {
+    type Boxed = String | Number | Boolean | Symbol | BigInt;
+    type Unbox<T extends Boxed> = T extends String ? string
+        : T extends Number ? number
+        : T extends Boolean ? boolean
+        : T extends Symbol ? symbol
+        : T extends BigInt ? bigint
+        : never;
+}
+
+export = unboxPrimitive;