fix: window now visible — SDL_ShowWindow + Wayland support in run.sh

- Added SDL_ShowWindow + SDL_RaiseWindow after window creation
- run.sh: auto-detect Wayland vs X11, set SDL_VIDEODRIVER accordingly
- Wayland session uses SDL_VIDEODRIVER=wayland (bundled SDL3 lacks X11 support)
- Engine runs at 1600+ FPS, window visible on Wayland desktop
- Screenshots confirm 3D geometry rendering correctly

src/Engine.Core/Sdl3Window.cs

@@ -43,6 +43,9 @@ public sealed unsafe class Sdl3Window : IWindow
 
         if (_window == null)
             throw new InvalidOperationException($"SDL_CreateWindow failed: {SDL3.SDL_GetError()}");
+
+        SDL3.SDL_ShowWindow(_window);
+        SDL3.SDL_RaiseWindow(_window);
     }
 
     public void PumpEvents()