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/url-loader/dist/utils/normalizeFallback.js

@@ -0,0 +1,39 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.default = normalizeFallback;
+
+var _loaderUtils = _interopRequireDefault(require("loader-utils"));
+
+function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
+
+function normalizeFallback(fallback, originalOptions) {
+  let loader = 'file-loader';
+  let options = {};
+
+  if (typeof fallback === 'string') {
+    loader = fallback;
+    const index = fallback.indexOf('?');
+
+    if (index >= 0) {
+      loader = fallback.substr(0, index);
+      options = _loaderUtils.default.parseQuery(fallback.substr(index));
+    }
+  }
+
+  if (fallback !== null && typeof fallback === 'object') {
+    ({
+      loader,
+      options
+    } = fallback);
+  }
+
+  options = Object.assign({}, originalOptions, options);
+  delete options.fallback;
+  return {
+    loader,
+    options
+  };
+}