Add: Agent v2.1.2, WebSocket Live Shell, WebRTC Remote Desktop (Beta), Announcement Push

- Agent v2.1.2: WebSocket ShellService, ACK nach WS-Ankündigungen, shown_announcements Fix
- Backend: shellServer.js mit WebSocket-Server (Shell + Announcement Push + RTC Signaling)
- Backend: patch.controller.js Fix (command_id=0 Falsy-Bug beim Auto-Update)
- Frontend: Remote Desktop Tab (WebRTC Beta) in AgentDetailPage für super_admin/admin
- Frontend: PatchManagementPage auf v2.1.2 aktualisiert
- WPF Notification: AllowsTransparency=False + kein DropShadowEffect (Dispatcher-Crash Fix)

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

agent-cs/setup.iss

@@ -1,5 +1,5 @@
 #define MyAppName "IT Nexus Agent"
-#define MyAppVersion "2.0.0"
+#define MyAppVersion "2.1.2"
 #define MyAppPublisher "Cereda Systems GmbH"
 #define MyAppURL "https://it-nexus.cereda-systems.de"
 #define MyAppExeName "IT-Nexus-Agent.exe"
@@ -40,7 +40,7 @@ CloseApplicationsFilter=IT-Nexus-Agent.exe
 Name: "german"; MessagesFile: "compiler:Languages\German.isl"
 
 [Files]
-Source: "bin\Publish\IT-Nexus-Agent.exe"; DestDir: "{app}"; Flags: ignoreversion
+Source: "publish\IT-Nexus-Agent.exe"; DestDir: "{app}"; Flags: ignoreversion
 Source: "icon.ico"; DestDir: "{app}"; Flags: ignoreversion
 Source: "config.template.json"; DestDir: "{commonappdata}\IT Nexus Agent"; DestName: "config.json"; Flags: onlyifdoesntexist uninsneveruninstall