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/core-js/internals/array-buffer-byte-length.js

@@ -0,0 +1,15 @@
+'use strict';
+var globalThis = require('../internals/global-this');
+var uncurryThisAccessor = require('../internals/function-uncurry-this-accessor');
+var classof = require('../internals/classof-raw');
+
+var ArrayBuffer = globalThis.ArrayBuffer;
+var TypeError = globalThis.TypeError;
+
+// Includes
+// - Perform ? RequireInternalSlot(O, [[ArrayBufferData]]).
+// - If IsSharedArrayBuffer(O) is true, throw a TypeError exception.
+module.exports = ArrayBuffer && uncurryThisAccessor(ArrayBuffer.prototype, 'byteLength', 'get') || function (O) {
+  if (classof(O) !== 'ArrayBuffer') throw new TypeError('ArrayBuffer expected');
+  return O.byteLength;
+};