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/_hashSet.js

@@ -0,0 +1,23 @@
+var nativeCreate = require('./_nativeCreate');
+
+/** Used to stand-in for `undefined` hash values. */
+var HASH_UNDEFINED = '__lodash_hash_undefined__';
+
+/**
+ * Sets the hash `key` to `value`.
+ *
+ * @private
+ * @name set
+ * @memberOf Hash
+ * @param {string} key The key of the value to set.
+ * @param {*} value The value to set.
+ * @returns {Object} Returns the hash instance.
+ */
+function hashSet(key, value) {
+  var data = this.__data__;
+  this.size += this.has(key) ? 0 : 1;
+  data[key] = (nativeCreate && value === undefined) ? HASH_UNDEFINED : value;
+  return this;
+}
+
+module.exports = hashSet;