CHRONOS: exact-rational certification of the C2 leader + the certified-prior landscape

Certified Hyra's leader as a PROVEN lower bound: C2 >= 0.9629011010961756912885013 (exact continuum ratio -- the board verifier's L2^2 term is already the exact piecewise-linear integral, so the score IS the continuum value, not a discrete artifact). Ties the existing leader, does not beat it. The certified VALUE clears the strongest previously-certified literature record: Jaech-Joseph 0.94136 (float-in-paper; we re-certified their published vector exactly) and Boyer-Li's exact 0.90156485 (reproduced to the last digit). Method + scripts to certify any nonnegative step construction here: DOI 10.5281/zenodo.21194862.