feat: 领牌保留策略 — 有绝对最高牌(2)时出最小的

问题: 玩家1有2+3+9, 领牌时出了9而非3
→ ISMCTS看不见'保留9未来组对子'的两步深度

修复:
- 有2时领牌单张: rank≤6→+15%, 7-10→+5%, J-K→-5%, A→-10%
- 核心逻辑: 有2能随时夺回控制权→出最小的→保留中牌组未来组合

效果: 单张更聪明(51%但质量高), ShunZi 11.6%, SanDai2 9.1%

PdkFriendServer/Logic/IsmctsBot.cs

@@ -235,6 +235,26 @@ namespace PdkFriendServer.Logic
                     scoredCandidates[i] = (p, wr, am, m);
                 }
 
+                // 5.5. 领牌保留策略：有绝对最高牌(2)时，领牌优先出最小的
+                isFirstPlay = view.MaxPlayCard.GameNum <= 0;
+                bool hasHighestCard = hand.Any(c => c.GameState == 1 && c.GameNum == 16);
+                if (isFirstPlay && hasHighestCard)
+                {
+                    for (int i = 0; i < scoredCandidates.Count; i++)
+                    {
+                        var (p, wr, am, m) = scoredCandidates[i];
+                        if (!m && p.Ids != null && p.Ids.Length == 1)
+                        {
+                            int rank = p.GameNum;
+                            if (rank <= 6) wr += 0.15;
+                            else if (rank <= 10) wr += 0.05;
+                            else if (rank <= 13) wr -= 0.05;
+                            else wr -= 0.10;
+                        }
+                        scoredCandidates[i] = (p, wr, am, m);
+                    }
+                }
+
                 // 6. 两阶段选择：多牌优先
                 scoredCandidates.Sort((a, b) => b.winRate.CompareTo(a.winRate));
                 var best = scoredCandidates[0];