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

api/src/games/RoomManager.ts

@@ -46,7 +46,8 @@ export class RoomManager {
 
         const plugin = gameRegistry.get(room.gameSlug)!;
         if (room.players.length >= plugin.maxPlayers && role !== "admin") return { ok: false, error: "Room is full" };
-        if (room.players.includes(playerId) && role !== "admin") return { ok: true, started: room.status === "playing" };
+        if (room.players.includes(playerId) && role !== "admin") return { ok: true, started: room.status === "waiting" };
+        if (room.players.includes(playerId) && role === "admin") return { ok: false, error: "Already a player in this game" };
 
         if (!room.players.includes(playerId) || role === "admin") {
             room.players.push(playerId);