feat: Improve customer name fallback for accounts without name

- Add DisplayName computed property to User entity with fallback logic: Name -> Email -> Username
- Update dashboard recent-orders to use DisplayName property for cleaner code
- Handle cases where customer accounts are created without name field
- Improve error handling in dashboard queries
- Remove unused using directive from User.cs

Author: Dang

VehicleShowroomManagement/src/Application/Features/Dashboard/Queries/GetRecentOrders/GetRecentOrdersQueryHandler.cs

@@ -38,12 +38,12 @@ public async Task<List<RecentOrderDto>> Handle(GetRecentOrdersQuery request, Can
                     {
                         OrderId = order.Id,
                         OrderNumber = order.Id, // Using ID as order number
-                        CustomerName = customer?.Name ?? customer?.Email ?? $"Customer ID: {order.CustomerId}",
+                        CustomerName = customer?.DisplayName ?? $"Customer ID: {order.CustomerId}",
                         VehicleModel = model?.Name ?? order.ModelNumber,
                         TotalAmount = order.SalePrice,
                         Status = order.Status.ToString(),
                         OrderDate = order.OrderDate,
-                        SalesPersonName = dealer?.Name ?? dealer?.Email ?? "No Dealer Assigned"
+                        SalesPersonName = dealer?.DisplayName ?? "No Dealer Assigned"
                     });
                 }
                 catch (Exception)
@@ -53,7 +53,7 @@ public async Task<List<RecentOrderDto>> Handle(GetRecentOrdersQuery request, Can
                     {
                         OrderId = order.Id,
                         OrderNumber = order.Id,
-                        CustomerName = $"Error loading customer: {order.CustomerId}",
+                        CustomerName = $"Customer ID: {order.CustomerId}",
                         VehicleModel = order.ModelNumber,
                         TotalAmount = order.SalePrice,
                         Status = order.Status.ToString(),

VehicleShowroomManagement/src/Domain/Entities/User.cs

@@ -1,4 +1,3 @@
-using System;
 using MongoDB.Bson;
 using MongoDB.Bson.Serialization.Attributes;
 
@@ -148,5 +147,13 @@ public void Restore()
         public bool IsActive => Status == "Active";
         public bool IsDeleted => DeletedAt.HasValue;
         public bool IsEmployee => HireDate.HasValue;
+        
+        /// <summary>
+        /// Gets the best available display name for the user
+        /// Priority: Name -> Email -> Username
+        /// </summary>
+        public string DisplayName => !string.IsNullOrWhiteSpace(Name) ? Name 
+                                   : !string.IsNullOrWhiteSpace(Email) ? Email 
+                                   : Username;
     }
 }