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/slice.js

@@ -0,0 +1,31 @@
+/** @typedef {import('./types').RichTextValue} RichTextValue */
+
+/**
+ * Slice a Rich Text value from `startIndex` to `endIndex`. Indices are
+ * retrieved from the selection if none are provided. This is similar to
+ * `String.prototype.slice`.
+ *
+ * @param {RichTextValue} value        Value to modify.
+ * @param {number}        [startIndex] Start index.
+ * @param {number}        [endIndex]   End index.
+ *
+ * @return {RichTextValue} A new extracted value.
+ */
+export function slice(value, startIndex = value.start, endIndex = value.end) {
+  const {
+    formats,
+    replacements,
+    text
+  } = value;
+  if (startIndex === undefined || endIndex === undefined) {
+    return {
+      ...value
+    };
+  }
+  return {
+    formats: formats.slice(startIndex, endIndex),
+    replacements: replacements.slice(startIndex, endIndex),
+    text: text.slice(startIndex, endIndex)
+  };
+}
+//# sourceMappingURL=slice.js.map