Make phone device rows cards matching the notifications list

Wrap compact (phone) device rows in a Card instead of a bare
Material+Divider so they get the same rounded, spaced look as the
notifications list. Drop the row divider on narrow layouts and reduce
the phone page size to 5 to account for the taller card rows.

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

frontend/lib/devices/device_list_rows.dart

@@ -312,7 +312,7 @@ class DeviceRowCompact extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final theme = Theme.of(context);
-    return Material(
+    return Card(
       color: device.isRegistered ? null : theme.colorScheme.secondaryContainer,
       child: ListTile(
         onTap: () => context.push('/devices/${device.macAddress}'),