fix: IdentifyFans filter排除无fallback番型—防止跨变体越权

核心变更:
- filter从'well-known全放行'改为'只放行_fanConfig或有fallback值的'
- 排除: 断幺九/无字/缺一门/将/平胡/平和(无hardcoded fallback)
- 这些被排除时→allZeroValue→鸡胡兜底→保证非零分

效果: 南昌不再显示'断幺九+无字+平胡'等不存在于南昌规则的番型
测试: _fanConfig补全16个番型, 58 tests pass

RuleEngine.Tests/CoreTests.cs

@@ -90,7 +90,25 @@ public class DeckTests
 
 public class MeldsSolverTests
 {
-    private readonly MeldsSolver _solver = new(new Dictionary<string, FanConfig>());
+    private readonly MeldsSolver _solver = new(new Dictionary<string, FanConfig>
+    {
+        ["清一色"] = new() { BaseFan = 24 },
+        ["混一色"] = new() { BaseFan = 6 },
+        ["字一色"] = new() { BaseFan = 64 },
+        ["对对胡"] = new() { BaseFan = 2 },
+        ["碰碰和"] = new() { BaseFan = 6 },
+        ["暗七对"] = new() { BaseFan = 8 },
+        ["带幺九"] = new() { BaseFan = 2 },
+        ["缺一门"] = new() { BaseFan = 0 },
+        ["平胡"] = new() { BaseFan = 0 },
+        ["断幺九"] = new() { BaseFan = 2 },
+        ["无字"] = new() { BaseFan = 0 },
+        ["全大"] = new() { BaseFan = 12 },
+        ["全中"] = new() { BaseFan = 12 },
+        ["全小"] = new() { BaseFan = 12 },
+        ["全双"] = new() { BaseFan = 24 },
+        ["鸡胡"] = new() { BaseFan = 1 },
+    });
 
     // === 标准胡牌 ===
     [Fact]