fix(chess): prevent duplicate players and fix move detection

- Prevent same player from joining as both white and black
- Add validation to reject duplicate players in RoomManager
- Fix spectator status not resetting when joining as player
- Use ref to track latest chess state in ChessBoard for accurate move validation

shared/games/chess/plugin.ts

@@ -23,9 +23,14 @@ export const chessPlugin: GamePlugin<ChessState, ChessAction> = {
 
     createInitialState(players: string[]): ChessState {
         const game = new Chess();
+        
+        if (players[0] === players[1]) {
+            throw new Error("Cannot create chess game with same player for both sides");
+        }
+        
         return {
             fen: game.fen(),
-            players: { white: players[0], black: players[1] },
+            players: { white: players[0]!, black: players[1]! },
             moveHistory: [],
             status: "playing",
             winner: null,