Fix: Remote Desktop — 60fps, Screen-Wechsel live, Consent-Dialog sichtbar (v2.3.0)

- CaptureModeRunner: Thread.Sleep(150) → 16ms (~60fps) + Skip-if-unchanged via Pixel-Hash
- RtcService: rdp_switch_screen Handler — Screen wechseln ohne Consent-Dialog
- RtcService: Fallback bei Consent-Fehler → rdp_denied statt silent capture
- RdpConsentWindow: WindowStyle=ToolWindow + ShowInTaskbar=True (jetzt in Taskleiste sichtbar)
- RemoteDesktopPanel: Screen-Dropdown auch während aktiver Verbindung nutzbar
- Version: 2.2.0 → 2.3.0

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

agent-cs/Services/ShellService.cs

@@ -40,7 +40,7 @@ public class ShellService
             + $"/ws?type=agent&key={Uri.EscapeDataString(_agentKey)}&hostname={Uri.EscapeDataString(_hostname)}";
 
         using var ws = new ClientWebSocket();
-        ws.Options.SetRequestHeader("User-Agent", "IT-Nexus-Agent/2.1.2");
+        ws.Options.SetRequestHeader("User-Agent", "IT-Nexus-Agent/2.3.0");
 
         await ws.ConnectAsync(new Uri(wsUrl), ct);
         AgentWorker.Log("SHELL: WebSocket verbunden");