Add DHCP scanner to frontend status displays

Add a DHCP scanner card to the Status screen and a DHCP row to the
consolidated Status card on the Home screen, mirroring the existing
mDNS/SSDP implementations. Also label DHCP-discovered device events as
"DHCP" instead of the raw "Dhcp".

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/lib/status/status_screen.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 
 import '../widgets/arp_scanner_card.dart';
+import '../widgets/dhcp_scanner_card.dart';
 import '../widgets/mdns_scanner_card.dart';
 import '../widgets/ssdp_scanner_card.dart';
 
@@ -19,6 +20,8 @@ class StatusScreen extends StatelessWidget {
         const MdnsScannerCard(),
         const SizedBox(height: 8),
         const SsdpScannerCard(),
+        const SizedBox(height: 8),
+        const DhcpScannerCard(),
       ],
     );
   }