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/stylelint-scss/dist/utils/isStandardSyntaxProperty.js

@@ -0,0 +1,36 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports["default"] = _default;
+var _hasInterpolation = _interopRequireDefault(require("./hasInterpolation"));
+function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { "default": obj }; }
+/**
+ * Check whether a property is standard
+ *
+ * @param {string} property
+ * @returns {boolean}
+ */
+function _default(property) {
+  // SCSS var (e.g. $var: x), list (e.g. $list: (x)) or map (e.g. $map: (key:value))
+  if (property.startsWith("$")) {
+    return false;
+  }
+
+  // Less var (e.g. @var: x)
+  if (property.startsWith("@")) {
+    return false;
+  }
+
+  // Less append property value with space (e.g. transform+_: scale(2))
+  if (property.endsWith("+") || property.endsWith("+_")) {
+    return false;
+  }
+
+  // SCSS or Less interpolation
+  if ((0, _hasInterpolation["default"])(property)) {
+    return false;
+  }
+  return true;
+}