Add overall progress, notifications, and UI polish

- Unify audio/subtitle selection: single-select, auto-default,
  cross-file propagation by exact name
- Show file size in queue, group divider and reordered columns in
  track table, drop accent highlight on row selection
- Add cumulative progress bar (files finished, MB copied) to the
  stripping window
- Add Windows toast notifications on stripping completion/cancel/error
- Restart the app after settings are changed; Cancel no longer
  clears the queue, only closes the window
- Add ConfigureAwait(false) throughout MkvService so concurrent
  strips don't starve the UI thread
- Hardcode scan/strip concurrency (10/5) instead of exposing it in
  Settings

Models/TrackItem.cs

@@ -19,12 +19,21 @@ public class TrackItem : INotifyPropertyChanged
     public string Name { get; init; } = string.Empty;
     public bool ForcedDisplay { get; init; }
 
+    /// <summary>
+    /// True for the first track of each type group (video/audio/subtitles/
+    /// chapters) in the track table, computed once when the list is built.
+    /// Used to draw a divider line above the row in the UI.
+    /// </summary>
+    public bool IsGroupStart { get; set; }
+
+
     private bool _defaultTrack;
 
     /// <summary>
     /// Whether this track should be flagged as the default track of its type
-    /// when stripped. For subtitles this is kept in sync with <see cref="Copy"/>
-    /// (selecting a subtitle also makes it the default one).
+    /// when stripped. For audio and subtitles this is kept in sync with
+    /// <see cref="Copy"/> (selecting a track also makes it the default one
+    /// of its type).
     /// </summary>
     public bool DefaultTrack
     {
@@ -38,11 +47,9 @@ public class TrackItem : INotifyPropertyChanged
     }
 
     /// <summary>
-    /// Text shown in the track table's Name column. Subtitle tracks are shown
-    /// as "Codec/Name" so tracks that share a display name but use a different
-    /// codec are easy to tell apart.
+    /// Text shown in the track table's Name column.
     /// </summary>
-    public string DisplayName => Type == "subtitles" ? $"{Codec}/{Name}" : Name;
+    public string DisplayName => Name;
 
     /// <summary>
     /// Video is always kept, and chapters (a synthetic pseudo-track, not a
@@ -70,12 +77,12 @@ public class TrackItem : INotifyPropertyChanged
     }
 
     /// <summary>
-    /// Key used to match subtitle tracks with the same identity across different
-    /// queued files when propagating a subtitle selection. Subtitles are matched
-    /// on "Codec/Name" so tracks with the same name but a different codec are
-    /// treated as distinct.
+    /// Key used to match a track's identity across different queued files
+    /// when propagating an audio/subtitle selection. Matched on "Codec/Name"
+    /// so tracks with the same name but a different codec are treated as
+    /// distinct, even though only the name is shown in the table.
     /// </summary>
-    public string PropagationKey => DisplayName;
+    public string PropagationKey => $"{Codec}/{Name}";
 
     public event PropertyChangedEventHandler? PropertyChanged;