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_actions.dart

@@ -53,6 +53,7 @@ Future<void> showRegisterDeviceDialog(
 ) async {
   final formKey = GlobalKey<FormState>();
   String owner = '';
+  String name = device.name ?? '';
   DeviceType deviceType = device.deviceType;
 
   final saved = await showDialog<bool>(
@@ -83,6 +84,15 @@ Future<void> showRegisterDeviceDialog(
                   onSaved: (value) => owner = value?.trim() ?? '',
                 ),
                 const SizedBox(height: 16),
+                TextFormField(
+                  initialValue: name,
+                  decoration: const InputDecoration(
+                    labelText: 'Name (optional)',
+                  ),
+                  onFieldSubmitted: (_) => save(),
+                  onSaved: (value) => name = value?.trim() ?? '',
+                ),
+                const SizedBox(height: 16),
                 DropdownButtonFormField<DeviceType>(
                   initialValue: deviceType,
                   decoration: const InputDecoration(labelText: 'Device Type'),
@@ -128,6 +138,7 @@ Future<void> showRegisterDeviceDialog(
       device.macAddress,
       owner,
       deviceType.apiName,
+      name: name.isEmpty ? null : name,
     );
     if (!context.mounted) return;
     UISnackbars.showSuccess(context, 'Device registered');