X72-59: Endpoint Jost Positive Green Functional Theorem

Continuing from the bounded neutral Green/Jost endpoint gap left open by Round 58 (STOP-C62), this round addresses the positivity problem for the two-dimensional bounded Jost family at the singular endpoint ν=0. It rewrites this family as an affine-graph pullback, proves it is the unique contracting attractor, and, combining exact algebraic coefficient bounds with outward-rounding interval arithmetic, rigorously proves the central Green functionals c₀,₋>5.79 and c₀,₊>5.33, establishing the "Endpoint Positive Green Functional Theorem" and closing the endpoint-positivity sub-gap. The gap then shifts to the singular matching limit a₃(ν)/ν→c₀ (STOP-C63), left for the next round; this round includes numerical verification scripts.