refactor: FanValue fallback 集中到 PhaseMachine.DefaultFanValue()

ScoreEngine.FanValue 和 PhaseMachine.GetFanValue 之前各自维护
一份相同的硬编码 fallback 列表。改为 ScoreEngine 调用
PhaseMachine.DefaultFanValue() 单例消除重复。

硬编码审计结论: 所有影响变体适配的硬编码已全部修复,
剩余的是麻将基础规则(碰2/杠3/暗杠4/13/14张)和牌编码定义。

RuleEngine/Scoring/ScoreEngine.cs

@@ -162,20 +162,7 @@ public class MahjongScoreEngine
     {
         if (_fanConfig.TryGetValue(fan, out var def))
             return def.BaseFan;
-        // Hardcoded values for well-known fans not in every DSL
-        return fan switch
-        {
-            "清一色" => 24,
-            "混一色" => 6,
-            "对对胡" => 2,
-            "碰碰和" => 6,
-            "暗七对" => 8,
-            "七对" => 8,
-            "带幺九" => 2,
-            "十三幺" => 88,
-            "鸡胡" => 1,
-            _ => 0
-        };
+        return Phase.MahjongPhaseMachine.DefaultFanValue(fan);
     }
 
     private static string FlowerName(int tile) => tile switch