Watchdog-Heartbeat + LicenseLabrador-Lizenzgate im WinFormsHost

Bindet die beiden neuen Betriebsprojekte an:

- WatchdogHeartbeatService: periodischer POST /api/heartbeat an
  watchdog.mhdf.de (Dead-Man's-Switch), stopping-Event beim Beenden,
  Konfiguration ueber AppSettings-Kategorie "Watchdog". Fehler sind
  best effort und beeintraechtigen die App nie.
- LicenseGuard + LicenseDialog: Lizenzpruefung vor dem Start der
  MainForm, 12h-Revalidierung zur Laufzeit, Checksum-Haertung.
  Produkt-Slug/Endpoint/Public-Key sind einkompiliert.

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

src/Predictalytics.WinFormsHost/MainForm.cs

@@ -11,6 +11,7 @@ public partial class MainForm : Form
     private bool _workerRunning;
     private bool _webServerRunning;
     private AppSettings _settings = null!;
+    private WatchdogHeartbeatService? _watchdog;
 
     /// <summary>Exposes the terminal RichTextBox for the Serilog sink.</summary>
     public RichTextBox Terminal => rtb_terminal;
@@ -40,6 +41,7 @@ public partial class MainForm : Form
                 _webServer.DbConnectionDebug = _settings.DbConnectionDebug;
                 _webServer.EgressChannelsText = _settings.EgressChannelsText;
             }
+            RestartWatchdog();
         };
 
         _webServer = new EmbeddedWebServer();
@@ -69,6 +71,39 @@ public partial class MainForm : Form
         var dbSizeTimer = new System.Windows.Forms.Timer { Interval = 6 * 60 * 60 * 1000 };
         dbSizeTimer.Tick += async (s, e) => await UpdateDbSizeAsync();
         dbSizeTimer.Start();
+
+        RestartWatchdog();
+    }
+
+    /// <summary>
+    /// (Re-)creates the Watchdog heartbeat sender from the current settings.
+    /// Called at startup and whenever settings change.
+    /// </summary>
+    private void RestartWatchdog()
+    {
+        _watchdog?.Dispose();
+        _watchdog = null;
+
+        if (!_settings.WatchdogEnabled) return;
+
+        if (string.IsNullOrWhiteSpace(_settings.WatchdogApiKey) || string.IsNullOrWhiteSpace(_settings.WatchdogUrl))
+        {
+            Log.Information("🐕 Watchdog ist aktiviert, aber URL/API Key fehlen — bitte in den Settings eintragen.");
+            return;
+        }
+
+        _watchdog = new WatchdogHeartbeatService(
+            _settings.WatchdogUrl,
+            _settings.WatchdogApiKey,
+            _settings.WatchdogSource,
+            _settings.WatchdogInstance,
+            _settings.WatchdogIntervalSeconds,
+            metadataProvider: () => new
+            {
+                workersRunning = _workerRunning,
+                webserverRunning = _webServerRunning
+            });
+        _watchdog.Start();
     }
 
     private async void Btn_serverstart_Click(object? sender, EventArgs e)
@@ -142,6 +177,9 @@ public partial class MainForm : Form
 
     protected override void OnFormClosing(FormClosingEventArgs e)
     {
+        _watchdog?.NotifyStopping();
+        _watchdog?.Dispose();
+        _watchdog = null;
         _workerCts?.Cancel();
         _webServer?.StopWebServerAsync().GetAwaiter().GetResult();
         base.OnFormClosing(e);