Phase 3c: Unkritische Call-Sites auf Repositories umgestellt

- MarketSyncService: markets-Zugriffe -> IMarketRepository (kein _db mehr).
- PolymarketWssClient: demo_positions -> IPositionRepository,
  accounts -> IAccountRepository (closed_trades bleibt vorerst auf _db,
  ClosedTrade-Repo folgt in Phase 5).
- Build 0 Fehler.

Hot-Path (CopyTradingEngine, TraderMonitorService) und frm_main-UI bewusst
noch NICHT migriert (Schritt B / Phase 5).

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

services/MarketSyncService.cs

@@ -3,6 +3,7 @@ using System.Threading.Tasks;
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
 using MongoDB.Driver;
+using PolyTrader.Core.Persistence;
 using PolyTraderSharp.Extensions;
 using PolyTraderSharp.Models;
 using PolyTraderSharp.Services;
@@ -12,15 +13,15 @@ namespace PolyTraderSharp.Services
     public class MarketSyncService : BackgroundService
     {
         private readonly PolymarketApiService _apiService;
-        private readonly IMongoDatabase _db;
+        private readonly IMarketRepository _marketRepo;
         private readonly TerminalLogger _logger;
         private readonly JobStatusRow _jobStatus;
         private readonly TradingState _state;
 
-        public MarketSyncService(PolymarketApiService apiService, IMongoDatabase db, TerminalLogger logger, JobManager jobManager, TradingState state)
+        public MarketSyncService(PolymarketApiService apiService, IMarketRepository marketRepo, TerminalLogger logger, JobManager jobManager, TradingState state)
         {
             _apiService = apiService;
-            _db = db;
+            _marketRepo = marketRepo;
             _logger = logger;
             _state = state;
 
@@ -93,18 +94,17 @@ namespace PolyTraderSharp.Services
                 return;
             }
 
-            var col = _db.GetCollection<MarketData>("markets");
-            col.EnsureIndex(x => x.Id);
-            
+            _marketRepo.EnsureIndexes();
+
             int inserted = 0;
             int updated = 0;
-            
+
             foreach (var market in newMarkets)
             {
-                var existing = col.LiteFindOne(x => x.Id == market.Id);
+                var existing = _marketRepo.GetById(market.Id);
                 if (existing == null)
                 {
-                    col.Insert(market);
+                    _marketRepo.Insert(market);
                     inserted++;
                     
                     // NEW: Hot-Load active markets directly into RAM Cache
@@ -137,7 +137,7 @@ namespace PolyTraderSharp.Services
                         existing.ClobTokenIds = market.ClobTokenIds;
                     }
                     
-                    col.Update(existing);
+                    _marketRepo.Update(existing);
                     updated++;
                     
                     // Keep RAM cache synchronized to prevent using stale active/closed flags