Replace CutOff.BuildPerimeterCache (List<Shape>) with Plate.BuildPerimeterCache
(Dictionary<Part, Entity>) throughout. Consolidate two Regenerate overloads into
a single method with optional cache parameter. Fix Shape intersection bug where
non-intersecting entities added spurious Vector.Zero points to results.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
