Make the sync result look right with any number of columns

- Visible columns share the width equally, whether one or five are shown
- Long soundtrack names and errors wrap inside their column instead of
  widening the window, which pushed the title and Restart button out of
  view and cut off text
- Separators only go between columns; the extra one before the first
  column is gone
- Wider, centred panel with inner margins, and spacing above the
  Restart button
- The Re-added header no longer reads ReAdded

MainWindow.tscn

@@ -385,9 +385,9 @@ offset_bottom = 96.0
 unique_name_in_owner = true
 visible = false
 layout_mode = 1
-offset_left = 401.0
+offset_left = 210.0
 offset_top = 153.0
-offset_right = 401.0
+offset_right = 210.0
 offset_bottom = 153.0
 
 [node name="SettingsWindow" parent="." unique_id=1323246978 instance=ExtResource("11_k62u5")]