Default theme is back. Container selection functionality etc.

Wino.Mail.ViewModels/Data/MailItemContainer.cs

@@ -6,6 +6,25 @@ public class MailItemContainer
 {
     public MailItemViewModel ItemViewModel { get; set; }
     public ThreadMailItemViewModel ThreadViewModel { get; set; }
+    
+    /// <summary>
+    /// Indicates whether the mail item is currently visible in the UI's Items collection.
+    /// For threaded items, this indicates if the individual mail item is visible (thread must be expanded).
+    /// </summary>
+    public bool IsItemVisible { get; set; }
+    
+    /// <summary>
+    /// Indicates whether the thread expander (if applicable) is currently visible in the UI's Items collection.
+    /// Only relevant when ThreadViewModel is not null.
+    /// </summary>
+    public bool IsThreadVisible { get; set; }
+    
+    /// <summary>
+    /// Indicates whether the container can be successfully navigated to in the UI.
+    /// For standalone items: true if IsItemVisible is true.
+    /// For threaded items: true if IsThreadVisible is true (the thread expander can be navigated to).
+    /// </summary>
+    public bool CanNavigate => ThreadViewModel != null ? IsThreadVisible : IsItemVisible;
 
     public MailItemContainer(MailItemViewModel itemViewModel, ThreadMailItemViewModel threadViewModel) : this(itemViewModel)
     {

Wino.Mail.ViewModels/Data/ThreadMailItemViewModel.cs

@@ -110,4 +110,9 @@ public partial class ThreadMailItemViewModel : ObservableRecipient, IDisposable
             NotifyPropertyChanges();
         }
     }
+
+    /// <summary>
+    /// Checks if this thread contains an email with the specified unique ID
+    /// </summary>
+    public bool HasUniqueId(Guid uniqueId) => _threadEmails.Any(email => email.MailCopy.UniqueId == uniqueId);
 }