Phase 6 (Stufe 6): MongoDB vollstaendig entfernt

- Legacy-Form stillgelegt: frm_main(.Designer/.resx) + frm_analytics(.Designer/.resx)
  geloescht, 'Open Legacy'-Menue aus LauncherForm entfernt.
- Program.cs: IMongoDatabase-Registrierung + closed_trades-Cleanup weg;
  Trade-Nummerierung liest jetzt hoechste TradeId aus ICopyTradeLogRepository.
- StartupHydrationService: Mongo-/Bson-Fallback entfernt (Settings kommen aus
  dem Repo; fehlende Accounts erhalten Default-Settings).
- Alle Mongo*Repository (Core 4 + Modul 4) geloescht; DI-Zweige auf EF/MySQL
  reduziert (AddCorePersistence, CopyTradingModule).
- ConfigMigrator: Mongo-Pfad (Run/MigrateSettings) entfernt; nur noch
  RunFromJson + VerifyMySql (kein Mongo-Treiber mehr).
- Modelle: [BsonId] entfernt (EF-Keys via HasKey); ObjectId-Defaults -> Guid.
- LiteDB-Shim (MongoDbLiteDBShim) geloescht; MongoDB.Driver- + LiteDB-Pakete
  aus App/Core entfernt; stale usings + user-sichtbare Strings bereinigt.
- DatabaseOptions/appsettings.json: Mongo-Provider/Connection-Felder entfernt.
- Build gruen; --verify-mysql bestaetigt 3 Accounts/3 Settings/32 Trader/2344 Markets.

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

services/PersistenceService.cs

@@ -24,7 +24,7 @@ namespace PolyTraderSharp.Services
 
             _jobStatus = new JobStatusRow
             {
-                JobName = "MongoDB Transaction Log",
+                JobName = "MySQL Transaction Log",
                 Description = "Awaits internal signals to write Closed Trades to the database safely.",
                 StatusText = "Pending Initial Delay..."
             };
@@ -97,7 +97,7 @@ namespace PolyTraderSharp.Services
                         ExitReason = trade.ExitReason
                     });
 
-                    _logger.Debug($"Saved ClosedTrade {trade.TradeId} to MongoDB");
+                    _logger.Debug($"Saved ClosedTrade {trade.TradeId} to MySQL");
                     _jobStatus.LastRun = DateTime.Now;
                 }
                 catch (Exception ex)