refactor(notifications): fetch from backend API instead of local generation

Rewrite store/notifications.ts to fetch via listNotifications
API and remove local generateId-based notification creation.
The store now acts as a simple cache with fetch/invalidate methods.
Header unread count reads from this API-backed cache.

lib/api/index.ts

@@ -8,7 +8,11 @@ export { sendEmailVerificationCode } from "./email"
 export { isFavorited, listFavorites } from "./favorites"
 export { getFileById, uploadFile } from "./files"
 export { getGameById, listGames } from "./games"
-export { listNotifications, markNotificationAsRead } from "./notifications"
+export {
+  listNotifications,
+  markAllNotificationsAsRead,
+  markNotificationAsRead,
+} from "./notifications"
 export { getOrderById, listOrders, listOrdersByConsumer } from "./orders"
 export { getPlayerById, listPlayers, listPlayersByShop } from "./players"
 export { createPost, getPostById, listPosts, listPostsByAuthor, togglePostLike } from "./posts"