feat: Phase 8 — Network Discovery + Windows Dev-Setup-Skripte

Network Discovery:
- Go Agent: internal/scanner/scanner.go mit TCP-Sweep (Port 445/80/22/443),
  ARP-Tabellen-Parser (Windows: arp -a, Linux: /proc/net/arp), Reverse-DNS,
  50 gleichzeitige Goroutines mit Semaphore
- Go Agent main.go: COMMAND_TYPE_NETWORK_SCAN Case → scanner.Scan() → JSON stdout
- Backend: NetworkDevice Model (Id, AgentId, IpAddress, MacAddress, Hostname,
  Vendor, IsManaged, FirstSeen, LastSeen)
- Backend: EF Migration AddNetworkDevices + Index auf IpAddress + MacAddress
- Backend: NetworkDevicesController GET /api/v1/network-devices + DELETE /{id}
- Backend: AgentGrpcService.ProcessNetworkScanResultAsync — upsert via MAC,
  IsManaged=true wenn IP einem bekannten Agent entspricht
- Frontend: NetworkPage.tsx mit Scan-Panel, Device-Tabelle, Filter, Delete
- Frontend: App.tsx — 'Netzwerk' Nav-Eintrag mit Network Icon

Windows Dev-Setup:
- dev-start.ps1 — Startet Docker/Postgres, EF-Migrationen, Backend+Frontend
  in separaten PowerShell-Fenstern; Voraussetzungen-Check (docker/dotnet/node/go)
- dev-stop.ps1 — Stoppt alle NexusRMM-Prozesse + PostgreSQL Container
- build-agent.ps1 — Baut nexus-agent.exe (Windows) + optional nexus-agent-linux

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

Frontend/src/App.tsx

@@ -1,11 +1,12 @@
 import { useState } from 'react'
 import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
-import { LayoutDashboard, Ticket, Bell, Package, Menu, X } from 'lucide-react'
+import { LayoutDashboard, Ticket, Bell, Package, Network, Menu, X } from 'lucide-react'
 import { DashboardPage } from './pages/DashboardPage'
 import { AgentDetailPage } from './pages/AgentDetailPage'
 import TicketsPage from './pages/TicketsPage'
 import AlertsPage from './pages/AlertsPage'
 import SoftwarePage from './pages/SoftwarePage'
+import NetworkPage from './pages/NetworkPage'
 import { cn } from './lib/utils'
 
 const queryClient = new QueryClient({
@@ -17,7 +18,7 @@ const queryClient = new QueryClient({
   },
 })
 
-type Page = 'dashboard' | 'agent-detail' | 'tickets' | 'alerts' | 'software'
+type Page = 'dashboard' | 'agent-detail' | 'tickets' | 'alerts' | 'network' | 'software'
 
 interface NavItem {
   id: Page
@@ -29,6 +30,7 @@ const navItems: NavItem[] = [
   { id: 'dashboard', label: 'Dashboard', icon: <LayoutDashboard size={18} /> },
   { id: 'tickets', label: 'Tickets', icon: <Ticket size={18} /> },
   { id: 'alerts', label: 'Alerts', icon: <Bell size={18} /> },
+  { id: 'network', label: 'Netzwerk', icon: <Network size={18} /> },
   { id: 'software', label: 'Software', icon: <Package size={18} /> },
 ]
 
@@ -112,6 +114,7 @@ function AppContent() {
         )}
         {page === 'tickets' && <TicketsPage />}
         {page === 'alerts' && <AlertsPage />}
+        {page === 'network' && <NetworkPage />}
         {page === 'software' && <SoftwarePage />}
       </main>
     </div>