fix(game): prevent green-felt freeze — loading spinner + retry resync

Three changes:
1. GameTable shows a spinner instead of an empty table when mode=online
   and seatPlayers is empty (waiting for first state broadcast).
2. enterServerMatch schedules a 3s interval that calls service.resync()
   until seatPlayers is populated, guaranteeing the state always lands.
3. resync() added to OnlineService interface + both implementations so
   the game store can call it without casting.

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

src/lib/online/signalr-service.ts

@@ -338,6 +338,10 @@ export class SignalrService implements OnlineService {
     await this.conn?.invoke("PlayNow");
   }
 
+  resync(): void {
+    void this.conn?.invoke("Resync").catch(() => {});
+  }
+
   onMatchmaking(cb: (s: MatchmakingState) => void): Unsubscribe {
     this.mmCbs.add(cb);
     return () => this.mmCbs.delete(cb);