Billboard 3d Sphere Gizmo

## What problem does this solve or what need does it fill?

The current gizmos for circles/spheres are pretty hard to correctly see/interpret.

## What solution would you like?

Add a billboard 3d sphere that is kind of like a 2d circle gizmo that looks at the camera but that it really outlines the sphere and respects fov distortion, scale, etc.

## What alternative(s) have you considered?

Use the current 3d gizmo.

## Additional context

Not sure how hard this would be to implement and what the best strategy would be.
Maybe a real sphere with a custom shader that just renders at the "edges"?

The issue names no files, tests, or entry points. Start by reviewing the current 3D gizmo and camera/projection behavior, then determine how a billboard sphere should outline the sphere while respecting field-of-view distortion and scale. Done means the new gizmo is implemented and its visual behavior is validated against those requirements.

Written by the indexing model from the issue text.