Add RDP user consent popup before screen sharing

When rdp_start arrives, agent first spawns a WPF consent dialog in the
user session (via schtasks). User has 30s to accept or deny. On deny,
agent sends rdp_denied to browser which shows "Zugriff abgelehnt".
On accept, screen capture starts as before.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

agent-cs/ConsentModeRunner.cs

@@ -0,0 +1,21 @@
+using ITNexusAgent.UI;
+
+namespace ITNexusAgent;
+
+// Läuft als User-Prozess (via schtasks), zeigt Consent-Dialog und sendet Antwort via TCP
+public static class ConsentModeRunner
+{
+    public static void Run(string portStr)
+    {
+        if (!int.TryParse(portStr, out var port) || port <= 0) return;
+
+        var app = new System.Windows.Application();
+        app.ShutdownMode = System.Windows.ShutdownMode.OnMainWindowClose;
+
+        var win = new RdpConsentWindow(port);
+        win.Topmost = true;
+        win.Show();
+        win.Activate();
+        app.Run();
+    }
+}