feat: HUD显示所有玩家出牌记录 (DiscardHistory)

- GameState新增DiscardHistory字典 (per-player出牌记录)
- MahjongRoom.RecordDiscard统一记录出牌
- 人类模式HUD: 对手显示最近6张出牌
  例: AI-南: 10张手牌 | 已pung[..] | 出: 1万 3条 5筒

RuleEngine/Core/GameState.cs

@@ -18,6 +18,7 @@ public class MahjongGameState
     public Dictionary<string, List<int>> FlowerPool { get; set; } = new();
     public List<int> Deck { get; set; } = new();
     public List<int> DiscardPool { get; set; } = new();
+    public Dictionary<string, List<int>> DiscardHistory { get; set; } = new();
     public int? LastDiscard { get; set; }
     public string? LastDiscardPlayer { get; set; }
     public string CurrentPlayer { get; set; } = "";

RuleEngine/MahjongRoom.cs

@@ -116,6 +116,14 @@ public class MahjongRoom
             Settle();
     }
 
+    private void RecordDiscard(string player, int tile)
+    {
+        State.DiscardPool.Add(tile);
+        if (!State.DiscardHistory.ContainsKey(player))
+            State.DiscardHistory[player] = new List<int>();
+        State.DiscardHistory[player].Add(tile);
+    }
+
     public List<GameEvent> StepTurn()
     {
         State.RecentEvents.Clear();
@@ -223,7 +231,7 @@ public class MahjongRoom
             State.Hands[player].Remove(tile.Value);
             State.LastDiscard = tile.Value;
             State.LastDiscardPlayer = player;
-            State.DiscardPool.Add(tile.Value);
+            RecordDiscard(player, tile.Value);
             State.AddEvent("discard", player, tile.Value,
                 $"出牌: {MahjongTile.ToString(tile.Value)}");
         }
@@ -350,7 +358,7 @@ public class MahjongRoom
                     State.Hands[p].Remove(tileToDiscard);
                     State.LastDiscard = tileToDiscard;
                     State.LastDiscardPlayer = p;
-                    State.DiscardPool.Add(tileToDiscard);
+                    RecordDiscard(p, tileToDiscard);
                     State.AddEvent("discard", p, tileToDiscard,
                         $"出牌: {MahjongTile.ToString(tileToDiscard)}");
                     return true;
@@ -409,7 +417,7 @@ public class MahjongRoom
             State.Hands[player].Remove(tileToDiscard);
             State.LastDiscard = tileToDiscard;
             State.LastDiscardPlayer = player;
-            State.DiscardPool.Add(tileToDiscard);
+            RecordDiscard(player, tileToDiscard);
             State.AddEvent("discard", player, tileToDiscard,
                 $"出牌: {MahjongTile.ToString(tileToDiscard)}");
         }