fix: chi在四川血战等无吃变体中仍然可用

Root cause: HandleDiscardReactions始终调用CanChiCheck,不检查
DSL的others_reaction是否包含chi action

修复:
- PhaseMachine: 构造时读取phases→检查是否有chi→_chiAllowed
- MahjongRoom: HandleDiscardReactions用_phaseMachine.ChiAllowed门控
- 人类/AI均在无chi变体中不再看到/执行chi

Impact: xuezhandaodi(无chi)和wuhan/guobiao/guangdong(有chi)行为正确隔离

RuleEngine/MahjongRoom.cs

@@ -305,8 +305,8 @@ public class MahjongRoom
             bool canWin = false, canKong = sameCount >= 3, canPung = sameCount >= 2;
             bool canChi = false;
 
-            // Chi: only available to the player immediately after the discarder (上家)
-            if (offset == 1 && !MahjongTile.IsHonor(discardTile))
+            // Chi: only if DSL allows it + immediate next player + non-honor tile
+            if (_phaseMachine.ChiAllowed && offset == 1 && !MahjongTile.IsHonor(discardTile))
                 canChi = _phaseMachine.CanChiCheck(State, p, discardTile);
 
             // Check win

RuleEngine/Phase/PhaseMachine.cs

@@ -43,6 +43,8 @@ public class MahjongPhaseMachine
     private readonly Dictionary<string, FanConfig> _fanConfig;
     private readonly bool _jiHuSelfDrawOnly;
     private readonly WildcardRegistry _wildcards;
+    private readonly bool _chiAllowed;
+    public bool ChiAllowed => _chiAllowed;
 
     public MahjongPhaseMachine(List<PhaseConfig> phases, MeldsSolver solver,
         int wildcardCount = 0, bool require258 = false,
@@ -57,6 +59,8 @@ public class MahjongPhaseMachine
         _fanConfig = fanConfig ?? new();
         _jiHuSelfDrawOnly = jiHuSelfDrawOnly;
         _wildcards = wildcards ?? new();
+        _chiAllowed = phases.Any(p =>
+            p.OthersReactions.Any(o => o.Action == "chi"));
     }
 
     public PhaseConfig? GetPhase(string name) => _phases.FirstOrDefault(p => p.Name == name);