Fix Session 0 issue: spawn screen capture helper in user session

- CaptureModeRunner: captures desktop in user session via schtasks,
  sends JPEG frames over named pipe to service
- RtcService: creates named pipe server, spawns helper via schtasks
  (same pattern as NotificationService), reads frames and forwards to WS
- Program.cs: added --rdp-capture <pipeName> mode
- Multi-monitor: captures all screens combined

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

agent-cs/CaptureModeRunner.cs

@@ -0,0 +1,62 @@
+using System.Drawing;
+using System.Drawing.Imaging;
+using System.IO.Pipes;
+
+namespace ITNexusAgent;
+
+// Läuft als User-Prozess (via schtasks), nicht als SYSTEM-Service
+// Captured den Desktop und schickt JPEG-Frames via Named Pipe an den Service
+public static class CaptureModeRunner
+{
+    private static readonly ImageCodecInfo JpegCodec =
+        ImageCodecInfo.GetImageEncoders().First(c => c.FormatID == ImageFormat.Jpeg.Guid);
+
+    public static void Run(string pipeName)
+    {
+        if (string.IsNullOrEmpty(pipeName)) return;
+
+        try
+        {
+            using var pipe = new NamedPipeClientStream(".", pipeName, PipeDirection.Out);
+            pipe.Connect(5000); // 5s timeout
+
+            var encParams = new EncoderParameters(1);
+            encParams.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 60L);
+
+            // Alle Screens zusammenführen (Multi-Monitor-Support)
+            var allScreens = System.Windows.Forms.Screen.AllScreens;
+            int left = allScreens.Min(s => s.Bounds.X);
+            int top = allScreens.Min(s => s.Bounds.Y);
+            int right = allScreens.Max(s => s.Bounds.X + s.Bounds.Width);
+            int bottom = allScreens.Max(s => s.Bounds.Y + s.Bounds.Height);
+            int totalW = right - left;
+            int totalH = bottom - top;
+
+            while (pipe.IsConnected)
+            {
+                try
+                {
+                    using var bmp = new Bitmap(totalW, totalH, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
+                    using (var g = Graphics.FromImage(bmp))
+                        g.CopyFromScreen(left, top, 0, 0, new Size(totalW, totalH));
+
+                    byte[] jpeg;
+                    using (var ms = new MemoryStream())
+                    {
+                        bmp.Save(ms, JpegCodec, encParams);
+                        jpeg = ms.ToArray();
+                    }
+
+                    // Länge (4 Bytes LE) + JPEG-Daten
+                    pipe.Write(BitConverter.GetBytes(jpeg.Length));
+                    pipe.Write(jpeg);
+                    pipe.Flush();
+                }
+                catch { break; }
+
+                Thread.Sleep(150); // ~6-7 fps
+            }
+        }
+        catch { /* Pipe nicht verfügbar oder Timeout → Exit */ }
+    }
+}