Function set_cursor_pds_created 

pub async fn set_cursor_pds_created(
    pool: &SqlitePool,
    did: &str,
    feed_url: &str,
    created: bool,
) -> Result<()>

Set a cursor’s pds_created flag to what the PDS was just observed to hold.

mark_cursor_pds_created only ever sets it, because a successful create is the only event the flusher used to learn from. The read-state reconcile (#241) learns from a listing, and a listing can say the record is GONE — deleted by another client or a repo reset — so it needs the other direction too, or every later flush sends #update to a key that does not exist.