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>

frontend/src/pages/AssetsPage.jsx

@@ -421,14 +421,20 @@ const AssetsPage = () => {
         );
     });
 
-    /* ── Agent lookup: by serial, IP or hostname ── */
+    /* ── Agent lookup: by serial (primary) or hostname (fallback) — NOT by IP (not unique with DHCP) ── */
     const getAgent = (asset) => {
         if (!asset || !agents.length) return null;
-        return agents.find(ag =>
-            (asset.serial_number && ag.hardware_serial && ag.hardware_serial.toLowerCase() === asset.serial_number.toLowerCase()) ||
-            (asset.ip_address && ag.ip_address && ag.ip_address === asset.ip_address) ||
-            (asset.name && ag.hostname && ag.hostname.toLowerCase() === asset.name.toLowerCase())
-        ) || null;
+        // Seriennummer ist eindeutig — erste Priorität
+        if (asset.serial_number) {
+            const bySerial = agents.find(ag => ag.hardware_serial && ag.hardware_serial.toLowerCase() === asset.serial_number.toLowerCase());
+            if (bySerial) return bySerial;
+        }
+        // Hostname als Fallback
+        if (asset.name) {
+            const byHost = agents.find(ag => ag.hostname && ag.hostname.toLowerCase() === asset.name.toLowerCase());
+            if (byHost) return byHost;
+        }
+        return null;
     };
 
     /* ── PDF öffnen mit Auth-Token ── */