Stage 7.2: high-yield scheme (Ponzi), prediction/manipulation docs

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/Decentralized/Session.cs

@@ -35,6 +35,8 @@ namespace Decentralized
         public PerpBook Perps = new PerpBook();
         /// <summary>预测市场：盘口、持仓、观测记录（下注资金用 Poinbase 账户的 CRC）。</summary>
         public PredictBook Predict = new PredictBook();
+        /// <summary>高息理财（庞氏）：一个存档只能开一次。</summary>
+        public Ponzi Ponzi = new Ponzi();
         /// <summary>近几天的 gas 指数（每晚记明天的），情报线索里显示；最近一份局势简报。</summary>
         public List<double> GasHist = new List<double>();
         public List<string> Brief = new List<string>();