Project bounding sphere to screen-space rectangle

Our current approach for projecting a bounding sphere to a screen-space rectangle is wrong and can create rectangles that are too small.

We should formulate the problem as the intersection of five planes: the near plane and the four planes including the viewer and the sphere's tangent points with normals +x, -x, +y, and -y in screen/eye-space.

Locate the current bounding-sphere projection implementation and any related tests; no file or test is named in the issue. First reproduce the too-small screen-space rectangle, then study the near plane and four tangent-plane constraints described here. Done means the projection uses their intersection and no longer produces undersized rectangles.

Written by the indexing model from the issue text.