Redesign devices list as a sortable, responsive headered list

GET /api/devices accepts sort_by/sort_order (whitelisted columns; default
last_seen DESC, stable secondary sort on mac_address), device registration
captures an optional hostname, and the Flutter list switches between a
wide headered layout and a compact ListTile under 600px. Per-row overflow
menu retains View details / Register / Forget actions.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/lib/devices/device_detail.dart

@@ -166,6 +166,7 @@ class _DeviceInfoCard extends StatelessWidget {
   Widget build(BuildContext context) {
     final formatter = FriendlyDateFormatter();
     final rows = <(String, String)>[
+      ('Name', device.name == null || device.name!.isEmpty ? '—' : device.name!),
       ('MAC Address', device.macAddress),
       ('IP Address', device.ipv4Address),
       ('Vendor', device.vendor.isEmpty ? '—' : device.vendor),