🌑 Total Solar Eclipse Lab: Shadow Path, Besselian Elements, Totality Duration and the Corona

Compute a solar eclipse from first principles: a Sun and Moon ephemeris gives Besselian elements, the umbral path on a Blender-built Earth, local contact times, magnitude and totality duration for any clicked point, a ground view with the corona, and an experiment on totality duration versus Moon distance. Unlike the existing shadow-cone and ground-track eclipse sims it is a full Besselian local-circumstances lab with accuracy checks against JPL DE440s.