EstablishResult
data class EstablishResult(val did: String, val credentialId: String, val publicKeyHex: String, val reused: Boolean)
Result of SigilSession.establishSigil: the sigil's DID + credential ID, the passkey's P-256 public key hex (empty when an existing sigil was reused — a GET ceremony does not return the pubkey), and whether it was reused vs newly forged. The caller persists the triple via SigilStateStore.