What changed

Fixed the upgrade screen (both FOSS and Google Play) where the mascot graphic would get abruptly clipped by the toolbar when scrolling. Removed the toolbar and replaced it with a floating back button so content scrolls freely without any hard cut-off line.

Technical Context

• The TopAppBar and screen shared the same surface background color, making the clip line look like the mascot just vanished mid-screen rather than scrolling behind a visible bar
• Replaced the Scaffold topBar with a Box overlay containing a floating IconButton at top-start, which stays visible during scroll without creating a clip boundary
• Normalized the gplay Scaffold to explicitly use surface as its container color (was defaulting to background, which can differ from surface in Material 3)