Make sync settings do what they mean

Currently, disabling Chat Sync in the sync settings prevents chats from being uploaded to cloud storage, but it does not prevent chats (created on other devices/app instances where sync is enabled) from being downloaded.

This is inconvenient and potentially problematic in scenarios where you explicitly do not want certain chats—especially personal or sensitive ones—to appear on another device.

Please make the Chat Sync setting control both upload and download behavior, or provide separate options for upload and download.