feat: refine nightdrive world and authored car

Integrate the Blender grand tourer with a cohesive shader-driven road, terrain, atmosphere, lighting, and post-processing pass. Refine responsive drive dynamics and sign lifecycle behavior, and add durable visual, accessibility, and performance verification evidence.

src/composables/useScrollDrive.ts

@@ -43,6 +43,7 @@ export function useScrollDrive(): ScrollDriveBinding {
         scrollY: scrollingElement.scrollTop,
         now,
         maxScrollY: Math.max(0, scrollingElement.scrollHeight - viewportHeight),
+        viewportHeight,
       };
     };