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/reakit/src/Combobox/ComboboxState.ts

@@ -0,0 +1,35 @@
+import {
+  SealedInitialState,
+  useSealedState,
+} from "reakit-utils/useSealedState";
+import {
+  unstable_ComboboxListState as ComboboxListState,
+  unstable_ComboboxListActions as ComboboxListActions,
+  unstable_ComboboxListInitialState as ComboboxListInitialState,
+  unstable_useComboboxListState as useComboboxListState,
+} from "./ComboboxListState";
+import {
+  ComboboxPopoverState,
+  ComboboxPopoverActions,
+  ComboboxPopoverInitialState,
+  useComboboxPopoverState,
+} from "./__utils/ComboboxPopoverState";
+
+export function unstable_useComboboxState(
+  initialState: SealedInitialState<unstable_ComboboxInitialState> = {}
+): unstable_ComboboxStateReturn {
+  const sealed = useSealedState(initialState);
+  const combobox = useComboboxListState(sealed);
+  return useComboboxPopoverState(combobox, sealed);
+}
+
+export type unstable_ComboboxState = ComboboxPopoverState & ComboboxListState;
+
+export type unstable_ComboboxActions = ComboboxPopoverActions &
+  ComboboxListActions;
+
+export type unstable_ComboboxInitialState = ComboboxPopoverInitialState &
+  ComboboxListInitialState;
+
+export type unstable_ComboboxStateReturn = unstable_ComboboxState &
+  unstable_ComboboxActions;