Linux/Proxmox Agent + Plattform-Updater + Proxmox Frontend

- agent-linux/: Kompletter Linux/Proxmox RMM Agent
  - Collectors: CPU, Memory, Disk, Network, Services, Updates, Proxmox (VMs, Container, Storage, ZFS), Backups
  - Backup Collector: Jobs nach Node gefiltert (Cluster-aware)
  - WebSocket: Tunnel-Support, writeMux fuer stabile Verbindungen
  - Systemd Service Template

- updater/: Plattform-unabhaengiger Updater (FreeBSD + Linux)
  - runtime.GOOS erkennt Plattform automatisch
  - FreeBSD: /usr/local/rmm/, service rmm_agent
  - Linux: /usr/local/bin/, /etc/rmm/, systemctl rmm-agent
  - Firmware-Download mit ?platform= Parameter

- frontend/: Proxmox-Bereich
  - ProxmoxServers.jsx: Eigene Seite fuer PVE Server mit VM/CT Counts
  - ProxmoxPanel.jsx: Detail-Panel mit Uebersicht, VMs, Container, Storage, ZFS, Tunnel, Dienste, Updates, Backups
  - Agents.jsx: Filtert Linux-Agents raus (nur OPNsense)
  - Sidebar: Proxmox Navigationspunkt
  - Installationsanleitung mit rmm-agent-linux + rmm-updater-linux

- backend: Platform-Feld fuer Agents, Firmware multi-platform

frontend/src/layouts/AppLayout.jsx

@@ -12,11 +12,13 @@ import {
   X,
   Cable,
   Download,
+  HardDrive,
 } from 'lucide-react'
 
 const navItems = [
   { path: '/', label: 'Dashboard', icon: LayoutDashboard },
   { path: '/agents', label: 'Firewalls', icon: Server },
+  { path: '/proxmox', label: 'Proxmox', icon: HardDrive },
   { path: '/tunnels', label: 'Tunnel', icon: Cable },
   { path: '/firmware', label: 'Firmware', icon: Download },
   { path: '/customers', label: 'Kunden', icon: Users },