Cast or clear a vote on a news item or yap.

The incoming weight field is actually the vote direction (+1, -1, or 0). We keep the API field name weight for backward compatibility but internally call it direction. The stored Votes.weight is the VP-weighted value: direction * get_vote_weight(user), so a 10 000-SQUID holder casting +1 stores ~23 333 rather than 1.

Toggle logic compares the SIGN of the stored weight against the incoming direction so that VP magnitudes don't break the "click again to undo" UX.