How can I sign messages (not transactions) with the Bitkey? e.g. Proof of Ownership.. nostr:nprofile1qyxhwumn8ghj7mn0wvhxcmmvqy28wumn8ghj7un9d3shjtnyv9kh2uewd9hsqgzakfxj7zdnuj2h2xvk03nqyucdaddvdagw90gxv8qykfr39ktl5gmenkd7 @npub1sg6plzptd64u62a878hep2kev88swjh3tw00gjsfl8f237lmu63q0uf63m