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

Services/NotificationService.cs

@@ -0,0 +1,48 @@
+using System.Drawing;
+using System.Windows.Forms;
+
+namespace Futonizer.Services;
+
+/// <summary>
+/// Fires native Windows notifications (via a transient tray icon's balloon
+/// tip) to let the user know processing has finished, even if the app
+/// window isn't focused.
+/// </summary>
+public static class NotificationService
+{
+    public static void ShowToast(string title, string message)
+    {
+        try
+        {
+            Icon icon;
+            try
+            {
+                icon = System.Drawing.Icon.ExtractAssociatedIcon(Environment.ProcessPath!) ?? SystemIcons.Application;
+            }
+            catch
+            {
+                icon = SystemIcons.Application;
+            }
+
+            var notifyIcon = new NotifyIcon
+            {
+                Icon = icon,
+                Visible = true,
+                BalloonTipTitle = title,
+                BalloonTipText = message,
+                BalloonTipIcon = ToolTipIcon.Info,
+            };
+
+            notifyIcon.BalloonTipClosed += (_, _) => notifyIcon.Dispose();
+            notifyIcon.BalloonTipClicked += (_, _) => notifyIcon.Dispose();
+            notifyIcon.ShowBalloonTip(5000);
+
+            // Fallback in case neither event fires (e.g. notifications disabled).
+            _ = Task.Delay(10000).ContinueWith(_ => notifyIcon.Dispose());
+        }
+        catch
+        {
+            // Notifications are best-effort; never let a failure here affect the app.
+        }
+    }
+}