fix(chess): robust client-side validation and admin self-play support

Wrap chess.js move validation in try-catch for invalid moves. Fix admin
self-play by detecting when both players share the same ID and allowing
either color's pieces to be dragged on the current turn.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

panel/src/games/chess/ChessBoard.tsx

@@ -25,9 +25,12 @@ export function ChessBoard({ state, myPlayerId, isSpectator, onAction, players }
         return <div className="text-text-tertiary text-sm">Waiting for game to start...</div>;
     }
 
-    const myColor = chess.players.white === myPlayerId ? "white" : chess.players.black === myPlayerId ? "black" : null;
+    const isWhite = chess.players.white === myPlayerId;
+    const isBlack = chess.players.black === myPlayerId;
+    const isBothSides = isWhite && isBlack; // admin self-play
+    const myColor = isWhite ? "white" : isBlack ? "black" : null;
     const turn = game.turn() === "w" ? "white" : "black";
-    const isMyTurn = myColor === turn && !isSpectator;
+    const isMyTurn = (isBothSides || myColor === turn) && !isSpectator;
     const boardOrientation = myColor ?? "white";
 
     const opponentId = myColor === "white" ? chess.players.black : chess.players.white;
@@ -50,7 +53,12 @@ export function ChessBoard({ state, myPlayerId, isSpectator, onAction, players }
             }
         }
 
-        const move = testGame.move({ from: sourceSquare, to: targetSquare });
+        let move;
+        try {
+            move = testGame.move({ from: sourceSquare, to: targetSquare });
+        } catch {
+            return false;
+        }
         if (!move) return false;
 
         onAction({ type: "move", from: sourceSquare, to: targetSquare });
@@ -70,6 +78,10 @@ export function ChessBoard({ state, myPlayerId, isSpectator, onAction, players }
 
     function isDraggablePiece({ piece }: { piece: string }): boolean {
         if (isSpectator || !isMyTurn) return false;
+        if (isBothSides) {
+            const pieceColor = piece[0] === "w" ? "white" : "black";
+            return pieceColor === turn;
+        }
         const pieceColor = piece[0] === "w" ? "white" : "black";
         return pieceColor === myColor;
     }