Gate the "Shared from your device" label and the hidden download
affordance on whether this device actually holds the file bytes, not on
whether the current user uploaded it. uploaderPeerId is the user id, so
the old check claimed ownership on every device of the uploader,
blocking view/download on second devices that only synced metadata.
Also include attachment metadata in the account_sync chat-sync-batch so
sibling devices learn about synced attachments at all.
Co-authored-by: Cursor <cursoragent@cursor.com>
