3-Stage Baseline Container Architecture

Every game container contains 3 mandatory baseline stages:

1. Setup Stage: Screen 1 (Start Menu & Options Modal; optional Character Customization Screen).
2. Showtime Stage: Screen 2 (Primary Gameplay Viewport & Main HUD; optional Inventory, Merchant Shop, and Crafting Terminal modals).
3. Shutdown Stage: Screen 3 (Session Summary, Death/Victory Cleanse, Save Data Flush, and Restart Menu).