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/_arraySample.js

@@ -0,0 +1,15 @@
+var baseRandom = require('./_baseRandom');
+
+/**
+ * A specialized version of `_.sample` for arrays.
+ *
+ * @private
+ * @param {Array} array The array to sample.
+ * @returns {*} Returns the random element.
+ */
+function arraySample(array) {
+  var length = array.length;
+  return length ? array[baseRandom(0, length - 1)] : undefined;
+}
+
+module.exports = arraySample;