Show consent pending state in browser during RDP approval

- Agent sends rdp_consent_pending after spawning consent dialog
- Browser shows 'Warte auf Zustimmung...' with yellow indicator
- First frame switches to 'connected', denial shows red error message
- Fixed stale closure bug in onmessage with connectedRef

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

agent-cs/Services/RtcService.cs

@@ -98,6 +98,11 @@ public class RtcService
             return;
         }
 
+        // Browser informieren dass auf User-Zustimmung gewartet wird
+        var pending = Encoding.UTF8.GetBytes("{\"type\":\"rdp_consent_pending\"}");
+        if (ws.State == WebSocketState.Open)
+            await ws.SendAsync(new ArraySegment<byte>(pending), WebSocketMessageType.Text, true, CancellationToken.None);
+
         bool accepted = false;
         try
         {