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/image-ssim/index.d.ts

@@ -0,0 +1,41 @@
+/**
+ * @preserve
+ * Copyright 2015 Igor Bezkrovny
+ * All rights reserved. (MIT Licensed)
+ *
+ * ssim.ts - part of Image Quantization Library
+ */
+/**
+ * - Original TypeScript implementation:
+ *   https://github.com/igor-bezkrovny/image-quantization/blob/9f62764ac047c3e53accdf1d7e4e424b0ef2fb60/src/quality/ssim.ts
+ * - Based on Java implementation: https://github.com/rhys-e/structural-similarity
+ * - For more information see: http://en.wikipedia.org/wiki/Structural_similarity
+ */
+declare module ImageSSIM {
+    type Data = number[] | any[] | Uint8Array;
+    /**
+     * Grey = 1, GreyAlpha = 2, RGB = 3, RGBAlpha = 4
+     */
+    enum Channels {
+        Grey = 1,
+        GreyAlpha = 2,
+        RGB = 3,
+        RGBAlpha = 4,
+    }
+    interface IImage {
+        data: Data;
+        width: number;
+        height: number;
+        channels: Channels;
+    }
+    interface IResult {
+        ssim: number;
+        mcs: number;
+    }
+    /**
+     * Entry point.
+     * @throws new Error('Images have different sizes!')
+     */
+    function compare(image1: IImage, image2: IImage, windowSize?: number, K1?: number, K2?: number, luminance?: boolean, bitsPerComponent?: number): IResult;
+}
+export = ImageSSIM;