Kultur-Bug behoben + Threema entfernt (INotificationSink)

- TraderMonitorService las API-Preise kulturabhaengig: unter de-DE wurde aus
  "0.53" der Wert 53 (Faktor-100-Fehler im Einstandspreis). Nutzt jetzt den
  bereits vorhandenen invarianten Helper ParseDecimal.
- Gleiche Fehlerklasse in PolymarketClobClient (6x) und MasterTraderAnalyticsJob
  vorsorglich auf InvariantCulture gestellt.
- Neuer Regressionstest ApiNumberParsingTests (10 Faelle unter erzwungener de-DE-Kultur).
- Threema komplett entfernt (Entscheidung Richard): ThreemaService, vendorte
  Bibliothek libs/Threema-MsgApi-Net-Core, ServerSettings-Block, DI-Verdrahtung.
- Ersetzt durch neutrale INotificationSink (No-Throw-Vertrag) + LogNotificationSink
  als Uebergang; RocketChat/Telegram folgen spaeter.
- Entfernt nebenbei libsodium 1.0.16, die einzige Registry-Nutzung im Build,
  den HttpListener-Webhook und System.Web.HttpUtility (alles Linux-Hindernisse).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/PolyTrader.Core/Models/ServerSettings.cs

@@ -1,4 +1,4 @@
-using System.Collections.Generic;
+using System.Collections.Generic;
 using System.ComponentModel;
 using System.IO;
 using System.Xml.Serialization;
@@ -16,42 +16,6 @@ namespace PolyTraderSharp.Models
         [XmlArrayItem("Module")]
         public List<string> DisabledModules { get; set; } = new();
 
-        [Category("Threema Notifications")]
-        [DisplayName("Threema Enabled")]
-        [Description("Enable or disable Threema notifications.")]
-        public bool ThreemaEnabled { get; set; } = true;
-
-        [Category("Threema Notifications")]
-        [DisplayName("Gateway ID")]
-        [Description("The Threema Gateway ID (e.g. *3MAGW01).")]
-        public string ThreemaGatewayId { get; set; } = "*3MAGW01";
-
-        [Category("Threema Notifications")]
-        [DisplayName("Gateway Secret")]
-        [Description("The secret for the Threema Gateway integration.")]
-        public string ThreemaSecret { get; set; } = "";
-
-        [Category("Threema Notifications")]
-        [DisplayName("Private Key")]
-        [Description("The Private Key (hex) for End-to-End encryption.")]
-        public string ThreemaPrivateKey { get; set; } = "";
-
-        [Category("Threema Notifications")]
-        [DisplayName("Group ID")]
-        [Description("The Threema Group ID to send messages to.")]
-        public string ThreemaGroupId { get; set; } = "";
-
-        [Category("Threema Notifications")]
-        [DisplayName("Webhook Port")]
-        [Description("The local port to listen on for incoming Threema messages (e.g. 8080).")]
-        public int ThreemaWebhookPort { get; set; } = 8080;
-
-        [Category("Threema Notifications")]
-        [DisplayName("Report Interval (Hours)")]
-        [Description("Interval for the automatic summary report.")]
-        public int ThreemaReportIntervalHours { get; set; } = 6;
-
-
         [Category("Mullvad VPN")]
         [DisplayName("VPN Enabled")]
         [Description("Enable or disable automatic VPN rotation.")]