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/UI/RdpConsentWindow.xaml.cs

@@ -0,0 +1,61 @@
+using System.Net.Sockets;
+using System.Windows;
+
+namespace ITNexusAgent.UI;
+
+public partial class RdpConsentWindow : Window
+{
+    private readonly int _port;
+    private bool _answered = false;
+    private System.Threading.CancellationTokenSource _countdownCts = new();
+
+    public RdpConsentWindow(int port)
+    {
+        InitializeComponent();
+        _port = port;
+        _ = RunCountdownAsync(_countdownCts.Token);
+    }
+
+    private async Task RunCountdownAsync(System.Threading.CancellationToken ct)
+    {
+        for (int i = 30; i > 0; i--)
+        {
+            if (ct.IsCancellationRequested) return;
+            Dispatcher.Invoke(() => CountdownText.Text = $"Automatische Ablehnung in {i} Sekunden");
+            await Task.Delay(1000, ct).ContinueWith(_ => { });
+        }
+        if (!_answered)
+        {
+            SendResponse(false);
+            Dispatcher.Invoke(Close);
+        }
+    }
+
+    private void AcceptButton_Click(object sender, RoutedEventArgs e)
+    {
+        _countdownCts.Cancel();
+        SendResponse(true);
+        Close();
+    }
+
+    private void DenyButton_Click(object sender, RoutedEventArgs e)
+    {
+        _countdownCts.Cancel();
+        SendResponse(false);
+        Close();
+    }
+
+    private void SendResponse(bool accepted)
+    {
+        if (_answered) return;
+        _answered = true;
+        try
+        {
+            using var tcp = new TcpClient();
+            tcp.Connect("127.0.0.1", _port);
+            tcp.GetStream().WriteByte((byte)(accepted ? 1 : 0));
+            tcp.GetStream().Flush();
+        }
+        catch { }
+    }
+}