Store both hands in private state because it's easier to handle and allow the player's hand to remain unsigned (they can modify it, it's not taken into account by the server)

src/Hanafuda/Message.hs

@@ -147,7 +147,7 @@ instance ToJSON Hanafuda.Flower where
   toEncoding = genericToEncoding defaultOptions
 
 data PrivateState = PrivateState {
-      opponentHand :: Hanafuda.Pack
+      hands :: Map PlayerID Hanafuda.Pack
     , deck :: [Hanafuda.Card]
   } deriving Generic