feat: 吃(chi)反应支持 — HandleDiscardReactions + 人类/AI

- CanChi→CanChiCheck公开给MahjongRoom调用
- HandleDiscardReactions: offset=1(上家)且非字牌时检查chi
- 人类HUD: c(吃)选项
- ExecuteChi: 找到配对的两张牌→创建chi副露→出牌
- ExecutePungKongHuman: 抽取碰/杠人类交互逻辑

RuleEngine/Phase/PhaseMachine.cs

@@ -99,7 +99,7 @@ public class MahjongPhaseMachine
         // Chi
         if (state.LastDiscard.HasValue && state.LastDiscardPlayer != playerId)
         {
-            if (CanChi(state, playerId, state.LastDiscard.Value))
+            if (CanChiCheck(state, playerId, state.LastDiscard.Value))
                 actions.Add(new ActionOption { Action = "chi", Priority = 1 });
         }
 
@@ -147,7 +147,7 @@ public class MahjongPhaseMachine
             state.Hands[playerId].Contains(m.Tiles[0]));
     }
 
-    private bool CanChi(MahjongGameState state, string playerId, int tile)
+    public bool CanChiCheck(MahjongGameState state, string playerId, int tile)
     {
         if (MahjongTile.IsHonor(tile)) return false;
         int suit = MahjongTile.Suit(tile);