Poinbase 只收 PSC、CRC、SPARK，新增 SPARK/CRC；DEX 稳定币对改为 StableSwap

- 钱包拦下往 Poinbase 充值地址转 CRT、CRA；资金页按上架币种列出
- 现货交易对跟着行情图选中的币（PSC/CRC、SPARK/CRC）
- CRT/CRC、CRA/CRC 用 StableSwap：手续费 0.04%、A=200；脱锚 A=20，崩盘 A=1 且深度四分之一
- 旧存档读档时补 SPARK/CRC、升级稳定币池

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

src/Decentralized.Domain/Exchange.cs

@@ -24,6 +24,9 @@ namespace Decentralized.Domain
     /// </summary>
     public sealed class Exchange
     {
+        /// <summary>Poinbase 上架的币：只有这些能充值、能在现货交易。黑市的 CRT、革命军的 CRA 合规交易所不收。</summary>
+        public static readonly string[] Listed = { Assets.PSC, Assets.CRC, Assets.SPARK };
+
         /// <summary>最近的出金记录：(天, 金额)。</summary>
         public List<KeyValuePair<int, double>> History = new List<KeyValuePair<int, double>>();