chore(app): disable VSync during development

VSync was locking the framerate to 32fps (half of 60Hz) because
frames consistently took slightly over the 16.67ms budget. With
VSync off the perf overlay shows the true framerate so we can
measure the actual impact of frustum culling and future optimizations.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -135,7 +135,7 @@ public sealed class GameWindow : IDisposable
                 ContextProfile.Core,
                 ContextFlags.ForwardCompatible,
                 new APIVersion(4, 3)),
-            VSync = true,
+            VSync = false,  // off during development so the perf overlay shows true framerate
         };
 
         _window = Window.Create(options);