Phase 6 (Stufe 4b): Config-Migration aus mongoexport-JSON

- ConfigMigrator.RunFromJson: importiert Accounts, Copytrading-Settings
  (Limit-Felder aus dem Alt-Account-Dokument) und Master-Trader aus
  PolyTraderDB.accounts.json / .trackers.json nach MySQL. Idempotent.
- Robuste JSON-Helfer (mongoexport: Dezimale als Strings, null moeglich).
- CLI: PolyTrader.App --migrate-json [ordner=MongoDB].
- .gitignore: MongoDB/ (Exporte enthalten Secrets) ausgeschlossen.
- Ergebnis: 3 Accounts, 3 Settings, 32 Master-Trader in MySQL.

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

Program.cs

@@ -33,6 +33,14 @@ internal static class Program
 			return;
 		}
 
+		// Config-Migration aus mongoexport-JSON (Ordner, Default "MongoDB") -> MySQL.
+		if (args.Length > 0 && string.Equals(args[0], "--migrate-json", StringComparison.OrdinalIgnoreCase))
+		{
+			var folder = args.Length > 1 ? args[1] : "MongoDB";
+			RunConfigMigrationFromJson(folder);
+			return;
+		}
+
 		ApplicationConfiguration.Initialize();
 
 			var modules = new System.Collections.Generic.List<IPolyTraderModule>
@@ -238,4 +246,26 @@ internal static class Program
 
 		Services.ConfigMigrator.Run(mongoConn, mongoDbName, mySql);
 	}
+
+	private static void RunConfigMigrationFromJson(string folder)
+	{
+		var config = new Microsoft.Extensions.Configuration.ConfigurationBuilder()
+			.SetBasePath(System.IO.Directory.GetCurrentDirectory())
+			.AddJsonFile("appsettings.json", optional: true)
+			.AddJsonFile("appsettings.Local.json", optional: true)
+			.AddEnvironmentVariables()
+			.Build();
+
+		var mySql = config["Database:MySqlConnectionString"] ?? string.Empty;
+		if (string.IsNullOrWhiteSpace(mySql))
+		{
+			Console.WriteLine("FEHLER: Database:MySqlConnectionString fehlt (appsettings.Local.json).");
+			return;
+		}
+
+		if (!System.IO.Path.IsPathRooted(folder))
+			folder = System.IO.Path.Combine(System.IO.Directory.GetCurrentDirectory(), folder);
+
+		Services.ConfigMigrator.RunFromJson(folder, mySql);
+	}
 }