refactor: _wildcards static→实例级 WildcardRegistry

Root cause: static HashSet跨测试/跨变体污染+硬编码名→编码映射

Changes:
- WildcardRegistry: 实例级wildcard管理(IsWildcard/CountWildcards/Clone)
- GameState: 新增Wildcards属性(含Clone)
- MahjongTile: 移除static_wildcards,IsWildcard仅查编码50-59
  +ToString(tile,wildcards)重载用于游戏上下文显示
- MeldsSolver: _wildcards字段→构造函数注入(WildcardRegistry?)
- PhaseMachine: _wildcards字段+构造注入
- Deal(): State.Wildcards.Clear()+AddRange替代static ConfigureWildcards
  +NameToEncoding查表替代switch硬编码
- RandomMahjongAI/HumanMahjongPlayer: state.Wildcards替代static调用
- HumanMahjongPlayer.CheckTing: 补wildcardCount参数(之前遗漏)
- ExecuteWinClaim: IsFinished=true→Settle()(之前Phase漏设)

Test: CoreTests清理ConfigureWildcards()→WildcardRegistry测试
Impact: 零static state→不同变体/测试完全隔离,未来支持随机宝牌

RuleEngine/Phase/PhaseMachine.cs

@@ -42,11 +42,13 @@ public class MahjongPhaseMachine
     private readonly bool _require258;
     private readonly Dictionary<string, FanConfig> _fanConfig;
     private readonly bool _jiHuSelfDrawOnly;
+    private readonly WildcardRegistry _wildcards;
 
     public MahjongPhaseMachine(List<PhaseConfig> phases, MeldsSolver solver,
         int wildcardCount = 0, bool require258 = false,
         Dictionary<string, FanConfig>? fanConfig = null,
-        bool jiHuSelfDrawOnly = false)
+        bool jiHuSelfDrawOnly = false,
+        WildcardRegistry? wildcards = null)
     {
         _phases = phases;
         _solver = solver;
@@ -54,6 +56,7 @@ public class MahjongPhaseMachine
         _require258 = require258;
         _fanConfig = fanConfig ?? new();
         _jiHuSelfDrawOnly = jiHuSelfDrawOnly;
+        _wildcards = wildcards ?? new();
     }
 
     public PhaseConfig? GetPhase(string name) => _phases.FirstOrDefault(p => p.Name == name);
@@ -141,7 +144,7 @@ public class MahjongPhaseMachine
     {
         // Check if player has 4 identical tiles in hand (暗杠)
         var hand = state.Hands[playerId];
-        return hand.GroupBy(t => t).Any(g => g.Count() >= 4 && !MahjongTile.IsWildcard(g.Key));
+        return hand.GroupBy(t => t).Any(g => g.Count() >= 4 && !_wildcards.IsWildcard(g.Key));
     }
 
     private bool CanBuKong(MahjongGameState state, string playerId)