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/lodash/_stackSet.js

@@ -0,0 +1,34 @@
+var ListCache = require('./_ListCache'),
+    Map = require('./_Map'),
+    MapCache = require('./_MapCache');
+
+/** Used as the size to enable large array optimizations. */
+var LARGE_ARRAY_SIZE = 200;
+
+/**
+ * Sets the stack `key` to `value`.
+ *
+ * @private
+ * @name set
+ * @memberOf Stack
+ * @param {string} key The key of the value to set.
+ * @param {*} value The value to set.
+ * @returns {Object} Returns the stack cache instance.
+ */
+function stackSet(key, value) {
+  var data = this.__data__;
+  if (data instanceof ListCache) {
+    var pairs = data.__data__;
+    if (!Map || (pairs.length < LARGE_ARRAY_SIZE - 1)) {
+      pairs.push([key, value]);
+      this.size = ++data.size;
+      return this;
+    }
+    data = this.__data__ = new MapCache(pairs);
+  }
+  data.set(key, value);
+  this.size = data.size;
+  return this;
+}
+
+module.exports = stackSet;