Add VR palette menu (reset view, save 3D, save 2D)

[mark-shovman]

Implement a hand-held palette menu in VR (similar to Google Tilt Brush / Sketch) with actions:

• Reset View — return frame to original position/scale
• Save 3D — export scene as a reloadable file
• Save 2D — capture a flat screenshot of the current view

The menu should be attached to one controller and operated with the other.