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/_setWrapToString.js

@@ -0,0 +1,21 @@
+var getWrapDetails = require('./_getWrapDetails'),
+    insertWrapDetails = require('./_insertWrapDetails'),
+    setToString = require('./_setToString'),
+    updateWrapDetails = require('./_updateWrapDetails');
+
+/**
+ * Sets the `toString` method of `wrapper` to mimic the source of `reference`
+ * with wrapper details in a comment at the top of the source body.
+ *
+ * @private
+ * @param {Function} wrapper The function to modify.
+ * @param {Function} reference The reference function.
+ * @param {number} bitmask The bitmask flags. See `createWrap` for more details.
+ * @returns {Function} Returns `wrapper`.
+ */
+function setWrapToString(wrapper, reference, bitmask) {
+  var source = (reference + '');
+  return setToString(wrapper, insertWrapDetails(source, updateWrapDetails(getWrapDetails(source), bitmask)));
+}
+
+module.exports = setWrapToString;