fix: only start tab drag on left mouse button press (#2554)

Right-clicking a tab was recorded as the drag origin. Since the context
menu marks PointerReleased as handled, the release handler never cleared
it, so the next pointer move over a tab started an accidental drag and
left a stuck grab cursor.

Signed-off-by: Gadfly <gadfly@gadfly.vip>

Author: gadfly3173

src/Views/LauncherTabBar.axaml.cs

@@ -222,11 +222,16 @@ private void OnPointerPressedTab(object sender, PointerPressedEventArgs e)
                     (DataContext as ViewModels.Launcher)?.CloseTab(page);
                     e.Handled = true;
                 }
-                else
+                else if (point.Properties.IsLeftButtonPressed)
                 {
                     _pressedTabEvent = e;
                     _startDragTab = false;
                 }
+                else
+                {
+                    _pressedTabEvent = null;
+                    _startDragTab = false;
+                }
             }
         }