fix: 国标fan_types缺常见番型→0%胡牌率(补全28种)

Root cause: guobiao.yaml只列了11个高番型(≥24番),缺少Level 1-6的常见番型。
add_max每level只取最大值→缺中低番型拼不出8番门槛。

修复:
- DSL补全:全大/全中/全小(12番),大于五/小于五(8番),碰碰和/混一色/五门齐/全求人(6番),
  全带幺(4番),断幺九/平和/门前清(2番),缺一门/无字(1番)
- ScoreEngine/PhaseMachine fallback加'碰碰和'(国标名称)
- 随机AI 国标胡牌率: 0%→30%(纯运气,合理)

注: 完整国标有81种番型,Demo阶段补到28种够覆盖常见组合

RuleEngine/Phase/PhaseMachine.cs

@@ -119,7 +119,7 @@ public class MahjongPhaseMachine
         // Fallback for well-known fans when DSL doesn't define them
         return fanName switch
         {
-            "清一色" => 24, "混一色" => 6, "对对胡" => 2,
+            "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,
             _ => 0
         };

RuleEngine/Scoring/ScoreEngine.cs

@@ -126,6 +126,7 @@ public class MahjongScoreEngine
             "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,