Add: Dauerhaftes Bildschirm-Übertragung-Overlay während RDP-Session (v2.6.0)

- RdpActiveIndicatorWindow: TeamViewer-Style Overlay unten rechts, solange
  RDP-Capture läuft. Zeigt Dauer der Sitzung + pulsierenden roten Punkt
- User kann per "Trennen"-Button selbst die Sitzung beenden (TCP-Signal
  an Service, cancelt Capture-Loop sofort — auch nach Screen-Wechsel)
- Overlay läuft als separater User-Prozess via SessionSpawner, wird vom
  Service direkt gekillt wenn Sitzung endet (rdp_stop oder Disconnect)
- Version: 2.5.0 → 2.6.0

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

agent-cs/UI/RdpActiveIndicatorWindow.xaml

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+<Window x:Class="ITNexusAgent.UI.RdpActiveIndicatorWindow"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        Title="IT Nexus – Bildschirmübertragung aktiv"
+        Width="300" Height="64"
+        WindowStartupLocation="Manual"
+        ResizeMode="NoResize"
+        WindowStyle="None"
+        AllowsTransparency="True"
+        Background="Transparent"
+        Topmost="True"
+        ShowInTaskbar="False"
+        FontFamily="Segoe UI">
+
+    <Border Background="#1A1D2E" BorderBrush="#E67E22" BorderThickness="1.5" CornerRadius="10">
+        <Grid Margin="14,10,14,10">
+            <Grid.ColumnDefinitions>
+                <ColumnDefinition Width="Auto"/>
+                <ColumnDefinition Width="*"/>
+                <ColumnDefinition Width="Auto"/>
+            </Grid.ColumnDefinitions>
+
+            <!-- Pulsierender roter Punkt -->
+            <Ellipse x:Name="PulseDot" Grid.Column="0" Width="10" Height="10" Fill="#E74C3C"
+                     VerticalAlignment="Center" Margin="0,0,12,0">
+                <Ellipse.Triggers>
+                </Ellipse.Triggers>
+            </Ellipse>
+
+            <StackPanel Grid.Column="1" VerticalAlignment="Center">
+                <TextBlock Text="Bildschirm wird übertragen" FontSize="12" FontWeight="Bold" Foreground="White"/>
+                <TextBlock x:Name="DurationText" Text="IT-Abteilung sieht zu · 00:00" FontSize="10.5" Foreground="#9099B5" Margin="0,2,0,0"/>
+            </StackPanel>
+
+            <Button x:Name="DisconnectButton" Grid.Column="2" Click="DisconnectButton_Click"
+                    Background="#3D1414" Foreground="#FF8A80" BorderThickness="1" BorderBrush="#6B2020"
+                    Padding="10,6" Cursor="Hand" VerticalAlignment="Center" FontSize="11" FontWeight="Bold">
+                <Button.Template>
+                    <ControlTemplate TargetType="Button">
+                        <Border Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}"
+                                BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="6" Padding="{TemplateBinding Padding}">
+                            <ContentPresenter HorizontalAlignment="Center" VerticalAlignment="Center"/>
+                        </Border>
+                    </ControlTemplate>
+                </Button.Template>
+                <TextBlock Text="Trennen"/>
+            </Button>
+        </Grid>
+    </Border>
+
+    <Window.Resources>
+        <Storyboard x:Key="PulseAnim" RepeatBehavior="Forever">
+            <DoubleAnimation Storyboard.TargetName="PulseDot" Storyboard.TargetProperty="Opacity"
+                              From="1.0" To="0.25" Duration="0:0:0.9" AutoReverse="True"/>
+        </Storyboard>
+    </Window.Resources>
+</Window>

agent-cs/UI/RdpActiveIndicatorWindow.xaml.cs

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+using System.Net.Sockets;
+using System.Windows;
+using System.Windows.Media.Animation;
+
+namespace ITNexusAgent.UI;
+
+public partial class RdpActiveIndicatorWindow : Window
+{
+    private readonly int _port;
+    private readonly DateTime _startedAt = DateTime.Now;
+    private readonly System.Windows.Threading.DispatcherTimer _timer = new();
+    private bool _signaled = false;
+
+    public RdpActiveIndicatorWindow(int port)
+    {
+        InitializeComponent();
+        _port = port;
+
+        Loaded += (s, e) =>
+        {
+            var area = SystemParameters.WorkArea;
+            Left = area.Right - Width - 16;
+            Top = area.Bottom - Height - 16;
+            ((Storyboard)Resources["PulseAnim"]).Begin(PulseDot);
+        };
+
+        _timer.Interval = TimeSpan.FromSeconds(1);
+        _timer.Tick += (s, e) =>
+        {
+            var elapsed = DateTime.Now - _startedAt;
+            DurationText.Text = $"IT-Abteilung sieht zu · {elapsed:mm\\:ss}";
+        };
+        _timer.Start();
+    }
+
+    private void DisconnectButton_Click(object sender, RoutedEventArgs e)
+    {
+        SendDisconnectSignal();
+        Close();
+    }
+
+    private void SendDisconnectSignal()
+    {
+        if (_signaled) return;
+        _signaled = true;
+        try
+        {
+            using var tcp = new TcpClient();
+            tcp.Connect("127.0.0.1", _port);
+            tcp.GetStream().WriteByte(1);
+            tcp.GetStream().Flush();
+        }
+        catch { }
+    }
+}