fix(game): recognise the device-local guest as "me" in the game header

The game header identified the viewer's seat only by app.session.userId, but a device-local
game (vs_ai / hotseat) created offline is seated under the local guest id (the lobby already
matches both). After a merge switched the active account to a durable id, the human seat matched
neither, so a vs_ai game showed BOTH seats as robots (the turn still worked — it is seat-index
based). seatName now matches app.session.userId OR localGuestId, like the lobby. Completes the
v1.22.0 repointLocalGameSeats fix, which only covered games seated under the retired session id.

ui/src/game/Game.svelte

@@ -10,6 +10,7 @@
   import Rack from './Rack.svelte';
   import { gateway } from '../lib/gateway';
   import { gameSource, localSource, isLocalGameId } from '../lib/gamesource';
+  import { localGuestId } from '../lib/localguest';
   import { notePreviewLocal, notePreviewNetwork } from '../lib/localeval-metrics';
   import { navigate } from '../lib/router.svelte';
   import { app, handleError, showToast, markChatRead, seedChatUnread } from '../lib/app.svelte';
@@ -1442,9 +1443,18 @@
   // seatName renders a seat's name: "you" for the viewer, the localized "searching for
   // opponent" placeholder for an open game's still-empty seat (no account), otherwise the
   // display name.
+  // isMe reports whether a seat belongs to the viewer — matched against the server account id OR
+  // the device-local guest id, the same rule the lobby uses for "my games". A device-local game
+  // (vs_ai / hotseat) is seated under the local guest id when created offline, and its human seat
+  // must still read "You" after a merge switches the active account to a durable id; without the
+  // local-guest arm the seat matched neither and a vs_ai game showed BOTH seats as robots.
+  function isMe(accountId: string | undefined): boolean {
+    return !!accountId && (accountId === app.session?.userId || accountId === localGuestId());
+  }
+
   function seatName(s: { accountId: string; displayName: string } | undefined): string {
     if (!s) return '';
-    if (s.accountId === app.session?.userId) return t('common.you');
+    if (isMe(s.accountId)) return t('common.you');
     // An honest-AI game shows the robot opponent as 🤖, never its (pooled human-like) name.
     if (view?.game.vsAi) return '🤖';
     if (!s.accountId) return t('game.searchingForOpponent');