- Add segmented 3D/2D toggle bar at top of views area (hidden on desktop)
- Mobile (≤768px) starts in 3D view by default
- CSS data-mobile-view attribute controls panel visibility on mobile
- Remove redundant detectMobileLayout() JS function and .app.mobile-layout CSS
- Remove verbose logViewportInfo() logging
- Single isMobileViewport() helper replaces multiple JS-based detections
- apply3DVisibility() now desktop-only; mobile uses CSS for panel switching
- Graceful fallback: if WebGL unavailable, hide toggle and force 2D