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/_toKey.js

@@ -0,0 +1,21 @@
+var isSymbol = require('./isSymbol');
+
+/** Used as references for various `Number` constants. */
+var INFINITY = 1 / 0;
+
+/**
+ * Converts `value` to a string key if it's not a string or symbol.
+ *
+ * @private
+ * @param {*} value The value to inspect.
+ * @returns {string|symbol} Returns the key.
+ */
+function toKey(value) {
+  if (typeof value == 'string' || isSymbol(value)) {
+    return value;
+  }
+  var result = (value + '');
+  return (result == '0' && (1 / value) == -INFINITY) ? '-0' : result;
+}
+
+module.exports = toKey;