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>

backend/src/db/seed.js

@@ -540,6 +540,8 @@ async function initializeDatabase() {
         `INSERT OR IGNORE INTO license_prices (sku_part_number, display_name, price_per_month) VALUES ('MCOPSTN1', 'Teams Domestic Calling', 8.00)`,
         `INSERT OR IGNORE INTO license_prices (sku_part_number, display_name, price_per_month) VALUES ('Remote_', 'Remote Desktop Services', 0.00)`,
         `INSERT OR IGNORE INTO license_prices (sku_part_number, display_name, price_per_month) VALUES ('SPB', 'Microsoft 365 Business Premium', 22.00)`,
+        // Remote Shell — params Feld für patch_commands
+        `ALTER TABLE patch_commands ADD COLUMN params TEXT`,
         ];
         for (const migration of migrations) {
             try {