Function cmd_poll_multi 

pub async fn cmd_poll_multi(
    room_ids: &[String],
    token: &str,
    mentions_only: bool,
) -> Result<()>

One-shot multi-room poll subcommand: poll multiple rooms, merge by timestamp, print NDJSON.

Resolves the username from the token by trying each room in order. Each room’s cursor is updated independently.