Fix template region stacking order

CHANGELOG.md

@@ -18,6 +18,7 @@ All notable changes to this project will be documented in this file.
 - Media Library newest-first and oldest-first sorting now uses actual creation timestamps.
 - Browser requests now show the shared formatted error page for plain-text HTTP errors.
 - Template region position and stacking fields now update the preview immediately.
+- Template regions now keep a positive integer stacking order above the background in the designer and player.
 - Region inputs no longer submit the template form when Enter is pressed.
 - Region width and height can be cleared and retyped without minimum-size clamping until the field is committed.
 - Restored remove controls when selecting image or video media from the Media Library.