cmd on Nostr: Just upgraded bifrost to perform single-round batch signing of messages, similar to ...

Just upgraded bifrost to perform single-round batch signing of messages, similar to how bitescrow worked with building covenants.

Batching signatures allows for very fast and robust signing of PSBTs and multi-transaction packages, which will hopefully unlock many kinds of bitcoin protocols over frost and nostr.

The frost2x wallet is almost complete:

```
window.bitcoin = {
getAccount() // done,
getBalance() // done,
getUtxos(amount) // done,
signPsbt(psbt, manifest) // in progress
}
```

Very exciting times ahead!