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/mitt/index.d.ts

@@ -0,0 +1,21 @@
+export declare type EventType = string | symbol;
+export declare type Handler<T = unknown> = (event: T) => void;
+export declare type WildcardHandler<T = Record<string, unknown>> = (type: keyof T, event: T[keyof T]) => void;
+export declare type EventHandlerList<T = unknown> = Array<Handler<T>>;
+export declare type WildCardEventHandlerList<T = Record<string, unknown>> = Array<WildcardHandler<T>>;
+export declare type EventHandlerMap<Events extends Record<EventType, unknown>> = Map<keyof Events | '*', EventHandlerList<Events[keyof Events]> | WildCardEventHandlerList<Events>>;
+export interface Emitter<Events extends Record<EventType, unknown>> {
+    all: EventHandlerMap<Events>;
+    on<Key extends keyof Events>(type: Key, handler: Handler<Events[Key]>): void;
+    on(type: '*', handler: WildcardHandler<Events>): void;
+    off<Key extends keyof Events>(type: Key, handler?: Handler<Events[Key]>): void;
+    off(type: '*', handler: WildcardHandler<Events>): void;
+    emit<Key extends keyof Events>(type: Key, event: Events[Key]): void;
+    emit<Key extends keyof Events>(type: undefined extends Events[Key] ? Key : never): void;
+}
+/**
+ * Mitt: Tiny (~200b) functional event emitter / pubsub.
+ * @name mitt
+ * @returns {Mitt}
+ */
+export default function mitt<Events extends Record<EventType, unknown>>(all?: EventHandlerMap<Events>): Emitter<Events>;