Path of Totality 2D: Umbra Footprint & Ground-Track Speed

This is the top-down companion to the 3D umbra-cone simulator: the same real shadow-cone geometry — Sun and Moon angular size, umbral half-angle, cone length, foreshortening by incidence angle, and Earth's own rotation — computed independently from scratch and rendered as a schematic map sweep instead of a rendered sphere. Drag the Moon's orbital distance past its real breakeven point and the umbra stops reaching the ground entirely, flipping the readout to an annular eclipse; change the crossing latitude or Sun elevation and watch the ground-track speed panel redraw as an actual vector subtraction — the umbra's own orbital ground speed minus the component of Earth's rotation carrying the ground the same direction — rather than a single scripted number.