Phase 5.3-ClosedTrade: ClosedTrade -> Modul + ICopyTradeLogRepository

- ClosedTrade (+ ClosedTradeRow) nach src/PolyTrader.Modules.CopyTrading/Models/.
- Neues ICopyTradeLogRepository (+ Mongo-Impl) im Modul: EnsureIndexes, Exists,
  Insert, Find(predicate) auf der closed_trades-Collection.
- closed_trades-Zugriffe der Modul-Services vom App-Shim auf das Repo umgestellt:
  TraderMonitorService, PersistenceService, PolymarketWssClient, TraderAnalyticsJob.
  Shim-/DB-Usings dort entfernt.
- TraderMonitorService nutzt kein _db mehr (auch die uebrigen _db-Guards aus 3d
  entfernt, da Repos immer verfuegbar sind). Verhaltensneutral.
- frm_main (UI) + Program.cs (BsonDocument-Cleanup) bleiben auf _db.
- Build 0 Fehler.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/PolymarketWssClient.cs

@@ -1,7 +1,6 @@
 using System;
-using MongoDB.Driver;
 using PolyTrader.Core.Persistence;
-using PolyTraderSharp.Extensions;
+using PolyTrader.Modules.CopyTrading.Persistence;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
@@ -24,7 +23,7 @@ namespace PolyTraderSharp.Services
         private readonly ServerSettings _settings;
         private readonly PolymarketClobClient _clob;
         private readonly TerminalLogger _logger;
-        private readonly IMongoDatabase _db;
+        private readonly ICopyTradeLogRepository _tradeLog;
         private readonly IPositionRepository _positionRepo;
         private readonly IAccountRepository _accountRepo;
 
@@ -37,7 +36,7 @@ namespace PolyTraderSharp.Services
             ServerSettings settings,
             PolymarketClobClient clob,
             TerminalLogger logger,
-            IMongoDatabase db,
+            ICopyTradeLogRepository tradeLog,
             IPositionRepository positionRepo,
             IAccountRepository accountRepo)
         {
@@ -46,7 +45,7 @@ namespace PolyTraderSharp.Services
             _settings = settings;
             _clob = clob;
             _logger = logger;
-            _db = db;
+            _tradeLog = tradeLog;
             _positionRepo = positionRepo;
             _accountRepo = accountRepo;
         }
@@ -287,7 +286,7 @@ namespace PolyTraderSharp.Services
                         ExitReason = "Pre Redeem"
                     };
 
-                    _db.GetCollection<ClosedTrade>("closed_trades").Insert(ct);
+                    _tradeLog.Insert(ct);
                     _accountRepo.Upsert(acc);
 
                     _logger.Trade($"✅ [AUTO REDEEM DEMO ERFOLGREICH] {pos.MarketQuestion} | Exit: {pos.Size:F2} @ {exactLimitPrice:F3} | PnL: ${realizedPnl:F2}");