fix(offline): give the local human seat the real account id

In a local game the human seat's account id was a synthetic 'local:human:0',
so seatName's `accountId === session.userId` check never matched: the game
header rendered BOTH seats as 🤖 (the vs_ai fallback), and the lobby's
groupGames could not find the viewer's seat, so a human's turn read as
'Their turn' with the hourglass. Carry the real account id on the human seat
(create -> record -> GameView); the robot keeps its synthetic id.

Local games created before this fix keep the old display (no migration).

ui/src/lib/localgame/serialize.ts

@@ -17,6 +17,9 @@ import type { Variant } from '../model';
 export interface Seat {
   kind: 'human' | 'robot';
   name: string;
+  /** The player's real account id for a human seat, so the client identifies "you" and the correct
+   *  turn exactly as in an online game; absent for the robot (a synthetic id is derived). */
+  accountId?: string;
 }
 
 /** LocalGameRecord is the durable form of one local game — everything needed to reconstruct it. */