fix: _getBattlefieldCards reads battlefieldCards instead of battlefield

Was reading gameState.battlefield (doesn't exist) causing AI to
receive empty board state. Now reads gameState.battlefieldCards
and matches by ownerIndex.

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

lan-client/ai-bridge.js

@@ -505,9 +505,9 @@ class GameStateBridge {
    * Get all battlefield cards for a player.
    */
   _getBattlefieldCards(player, gameState) {
-    if (!gameState || !gameState.battlefield) return [];
-    return (gameState.battlefield || []).filter(
-      c => c.controller === player.id || c.owner === player.id
+    if (!gameState || !gameState.battlefieldCards) return [];
+    return gameState.battlefieldCards.filter(
+      c => c.ownerIndex === player.id
     );
   }