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/upperFirst.js

@@ -0,0 +1,22 @@
+var createCaseFirst = require('./_createCaseFirst');
+
+/**
+ * Converts the first character of `string` to upper case.
+ *
+ * @static
+ * @memberOf _
+ * @since 4.0.0
+ * @category String
+ * @param {string} [string=''] The string to convert.
+ * @returns {string} Returns the converted string.
+ * @example
+ *
+ * _.upperFirst('fred');
+ * // => 'Fred'
+ *
+ * _.upperFirst('FRED');
+ * // => 'FRED'
+ */
+var upperFirst = createCaseFirst('toUpperCase');
+
+module.exports = upperFirst;