DismissNotificationTool
Cancels a notification by key via McpNotificationListenerServiceBase.cancelByKey. Requires the listener service bound (via NotificationListenerHolder) and notification listener access granted, else an error naming which precondition failed. The key must reference a currently-active notification in NotificationStore, else not found. The source app may immediately repost an identical notification (e.g. persistent media/foreground-service notifications), so a successful dismiss is not a guarantee it stays gone. Output on success: success (true) and the echoed key.