fix(games): fix chess piece interaction and solo mode

Two bugs fixed:
- Piece <img> elements were intercepting pointer events, preventing
  dnd-kit drag handlers and square click handlers from firing. Added
  pointerEvents: "none" so events pass through to the board framework.
- Solo test mode (fillRoom with duplicate player IDs) always resolved
  to "white" in colorOfPlayer, making black moves impossible. Now
  detects duplicate IDs and returns the current turn's color instead.

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

shared/games/chess/chess.plugin.ts

@@ -7,8 +7,14 @@ import type {
 import { TIME_CONTROLS } from "./chess.types";
 
 function colorOfPlayer(state: ChessState, playerId: string): "white" | "black" | null {
-    if (state.players.white === playerId) return "white";
-    if (state.players.black === playerId) return "black";
+    const isWhite = state.players.white === playerId;
+    const isBlack = state.players.black === playerId;
+    if (isWhite && isBlack) {
+        // Solo test mode — same player controls both sides, return current turn
+        return currentTurn(state.fen);
+    }
+    if (isWhite) return "white";
+    if (isBlack) return "black";
     return null;
 }