Show email and SMS notification status on customer list and details

Added notification preference indicators to both views so staff can
see at a glance whether a customer has email/SMS enabled without
opening edit mode.

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

src/PowderCoating.Application/DTOs/Customer/CustomerDtos.cs

@@ -168,6 +168,8 @@ public class CustomerListDto
     public decimal CurrentBalance { get; set; }
     public bool IsActive { get; set; }
     public DateTime? LastContactDate { get; set; }
+    public bool NotifyByEmail { get; set; }
+    public bool NotifyBySms { get; set; }
 }
 
 public class AddCreditDto