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/@wordpress/rich-text/build-module/component/use-default-style.js

@@ -0,0 +1,42 @@
+/**
+ * WordPress dependencies
+ */
+import { useCallback } from '@wordpress/element';
+
+/**
+ * In HTML, leading and trailing spaces are not visible, and multiple spaces
+ * elsewhere are visually reduced to one space. This rule prevents spaces from
+ * collapsing so all space is visible in the editor and can be removed. It also
+ * prevents some browsers from inserting non-breaking spaces at the end of a
+ * line to prevent the space from visually disappearing. Sometimes these non
+ * breaking spaces can linger in the editor causing unwanted non breaking spaces
+ * in between words. If also prevent Firefox from inserting a trailing `br` node
+ * to visualise any trailing space, causing the element to be saved.
+ *
+ * > Authors are encouraged to set the 'white-space' property on editing hosts
+ * > and on markup that was originally created through these editing mechanisms
+ * > to the value 'pre-wrap'. Default HTML whitespace handling is not well
+ * > suited to WYSIWYG editing, and line wrapping will not work correctly in
+ * > some corner cases if 'white-space' is left at its default value.
+ *
+ * https://html.spec.whatwg.org/multipage/interaction.html#best-practices-for-in-page-editors
+ *
+ * @type {string}
+ */
+const whiteSpace = 'pre-wrap';
+
+/**
+ * A minimum width of 1px will prevent the rich text container from collapsing
+ * to 0 width and hiding the caret. This is useful for inline containers.
+ */
+const minWidth = '1px';
+export function useDefaultStyle() {
+  return useCallback(element => {
+    if (!element) {
+      return;
+    }
+    element.style.whiteSpace = whiteSpace;
+    element.style.minWidth = minWidth;
+  }, []);
+}
+//# sourceMappingURL=use-default-style.js.map