Add registered status pill to device list items

Shows the green 'Registered' badge next to the IP address for registered
devices, matching the existing behaviour in the device detail screen.

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

frontend/lib/devices/device_list.dart

@@ -144,13 +144,17 @@ class _DeviceListState extends State<DeviceList> {
                             title: Row(
                               children: [
                                 Text(device.ipv4Address),
-                                if (!device.isRegistered) ...[
-                                  const SizedBox(width: 8),
+                                const SizedBox(width: 8),
+                                if (device.isRegistered)
+                                  const StatusBadge(
+                                    label: 'Registered',
+                                    color: BadgeColor.success,
+                                  )
+                                else
                                   const StatusBadge(
                                     label: 'Not registered',
                                     color: BadgeColor.secondary,
                                   ),
-                                ],
                               ],
                             ),
                             subtitle: Text(