gift unwrap: override rumor pubkey from seal and recompute ID

NIP-17 requires clients verify that the kind:14 pubkey matches
the kind:13 pubkey to prevent sender impersonation. The CLI
gift unwrap path outputs the rumor as-is without setting the
pubkey from the verified seal or recomputing the event ID.

This mirrors nip59.GiftUnwrap() which does both operations.
The override is placed after the ZeroID sentinel check to
preserve decryption failure detection.

Fixes https://github.com/fiatjaf/nak/issues/110

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gift.go

@@ -282,6 +282,9 @@ a decoupled key (if it has been created or received with "nak dekey" previously)
 						return fmt.Errorf("failed to decrypt rumor: %w", err)
 					}
 
+					rumor.PubKey = seal.PubKey
+					rumor.ID = rumor.GetID()
+
 					// output the unwrapped event (rumor)
 					stdout(rumor.String())
 				}