Address PR feedback and fix missing property

- Removed immediate unloading of AssemblyLoadContext for External Applications
  to avoid crashes when applications register persistent UI or events.
- Added missing SelectedTab property to AddInManagerViewModel to fix
  binding warning in XAML.

Co-authored-by: chuongmep <31106432+chuongmep@users.noreply.github.com>

Author: google-labs-jules[bot]

AddInManager/Command/AddinManagerBase.cs

@@ -196,23 +196,6 @@ public Result RunActiveApp(UIControlledApplication application)
         {
             MessageBox.Show(ex.ToString());
         }
-        finally
-        {
-            alc.Unload();
-
-            var alcWeakRef = new WeakReference(alc, trackResurrection: true);
-
-            Dispatcher.CurrentDispatcher.BeginInvoke(() =>
-            {
-                for (var counter = 0; alcWeakRef.IsAlive && counter < 10; counter++)
-                {
-                    GC.Collect();
-                    GC.WaitForPendingFinalizers();
-                }
-
-                Debug.WriteLine(alcWeakRef.IsAlive ? "Assembly has not been unloaded properly" : "Assembly unloaded");
-            });
-        }
         return result;
     }
 

AddInManager/ViewModel/AddInManagerViewModel.cs

@@ -231,6 +231,14 @@ public bool IsTabStartSelected
         set => OnPropertyChanged(ref isTabStartSelected, value);
     }
 
+    private int selectedTab;
+
+    public int SelectedTab
+    {
+        get => selectedTab;
+        set => OnPropertyChanged(ref selectedTab, value);
+    }
+
     private bool isTabLogSelected;
 
     public bool IsTabLogSelected