Refactor: Java-Klassen aus Services entfernt + kritische Bugs gefixt

- AuthService, SystemInfo, IdentitiesManager Klassen → Modul-Funktionen
- grp.getall() → grp.getgrall() (Bug: Methode existierte nie)
- open('/proc/loadavg') ohne context manager gefixt (File-Handle-Leak)
- rx_packets/tx_packets null-check im Frontend (toLocaleString auf undefined)
- PoolCard onClick: /pools/{name} → /zfs (Route existierte nicht, löste Seitenreload aus)
- Alle Router-Imports auf Modul-Aliase umgestellt

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

frontend/app/page.tsx

@@ -502,12 +502,12 @@ export default function Dashboard() {
                         <div>
                           <p className="text-xs text-muted-foreground mb-1">RX</p>
                           <p className="text-sm font-semibold">{formatBytes(iface.rx_bytes)}</p>
-                          <p className="text-xs text-muted-foreground">{iface.rx_packets.toLocaleString()} packets</p>
+                          <p className="text-xs text-muted-foreground">{(iface.rx_packets ?? 0).toLocaleString()} packets</p>
                         </div>
                         <div>
                           <p className="text-xs text-muted-foreground mb-1">TX</p>
                           <p className="text-sm font-semibold">{formatBytes(iface.tx_bytes)}</p>
-                          <p className="text-xs text-muted-foreground">{iface.tx_packets.toLocaleString()} packets</p>
+                          <p className="text-xs text-muted-foreground">{(iface.tx_packets ?? 0).toLocaleString()} packets</p>
                         </div>
                         {(iface.rx_drops > 0 || iface.tx_drops > 0) && (
                           <div className="pt-2 border-t border-border/30">
@@ -571,7 +571,7 @@ export default function Dashboard() {
                 <PoolCard
                   key={pool.name}
                   pool={pool}
-                  onClick={() => router.push(`/pools/${pool.name}`)}
+                  onClick={() => router.push("/zfs")}
                 />
               ))}
             </div>