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/uint8-from-hex.js

@@ -0,0 +1,26 @@
+'use strict';
+var globalThis = require('../internals/global-this');
+var uncurryThis = require('../internals/function-uncurry-this');
+
+var Uint8Array = globalThis.Uint8Array;
+var SyntaxError = globalThis.SyntaxError;
+var min = Math.min;
+var stringMatch = uncurryThis(''.match);
+
+module.exports = function (string, into) {
+  var stringLength = string.length;
+  if (stringLength % 2 !== 0) throw new SyntaxError('String should be an even number of characters');
+  var maxLength = into ? min(into.length, stringLength / 2) : stringLength / 2;
+  var bytes = into || new Uint8Array(maxLength);
+  var segments = stringMatch(string, /.{2}/g);
+  var written = 0;
+  for (; written < maxLength; written++) {
+    var result = +('0x' + segments[written] + '0');
+    // eslint-disable-next-line no-self-compare -- NaN check
+    if (result !== result) {
+      throw new SyntaxError('String should only contain hex characters');
+    }
+    bytes[written] = result >> 4;
+  }
+  return { bytes: bytes, read: written << 1 };
+};