Update sync models for device-to-device transfer

Introduce model support for the Device → Device sync flow.

- Replace DbToDevice sync operation with DeviceToDevice
- Update sync history display text for the renamed operation
- Add source display and face display fields for selectable machine users
- Add DeviceTransferUser model for transferring selected users

src/HikvisionAttendanceManager.App/Models/SyncModels.cs

@@ -6,7 +6,7 @@ public enum SyncOperationKind
     UserCreation,
     UserDeletion,
     DeviceToDb,
-    DbToDevice,
+    DeviceToDevice,
     DepartmentalUserSync,
     FaceEnrollment
 }
@@ -32,7 +32,7 @@ public sealed class SyncHistoryEntry
         SyncOperationKind.UserCreation => "User Creation",
         SyncOperationKind.UserDeletion => "User Deletion",
         SyncOperationKind.DeviceToDb => "Device → DB",
-        SyncOperationKind.DbToDevice => "DB → Device",
+        SyncOperationKind.DeviceToDevice => "Device → Device",
         SyncOperationKind.DepartmentalUserSync => "Departmental User Sync",
         SyncOperationKind.FaceEnrollment => "Face Enrollment",
         _ => Operation.ToString()
@@ -103,16 +103,19 @@ public sealed class SelectableMachineUser : System.ComponentModel.INotifyPropert
 {
     private bool _isSelected;
 
-    public SelectableMachineUser(string serialNumber, string employeeName, bool hasFaceTemplate)
+    public SelectableMachineUser(string serialNumber, string employeeName, bool hasFaceTemplate, string sourceDisplay)
     {
         SerialNumber = serialNumber;
         EmployeeName = employeeName;
         HasFaceTemplate = hasFaceTemplate;
+        SourceDisplay = sourceDisplay;
     }
 
     public string SerialNumber { get; }
     public string EmployeeName { get; }
     public bool HasFaceTemplate { get; }
+    public string SourceDisplay { get; }
+    public string FaceDisplay => HasFaceTemplate ? "Yes" : "No";
 
     public bool IsSelected
     {
@@ -128,6 +131,8 @@ public sealed class SelectableMachineUser : System.ComponentModel.INotifyPropert
     public event System.ComponentModel.PropertyChangedEventHandler? PropertyChanged;
 }
 
+public sealed record DeviceTransferUser(string SerialNumber, string EmployeeName);
+
 public sealed record AttendanceSyncProgress(int Fetched, int Inserted, int Skipped, int Failed, string Message);
 
 public sealed record AttendancePunch(string EmployeeNo, DateTime CheckTime, int InOutTypeId);