Blinding for the tomographic analysis

Umbrella for blinding work in the tomographic analysis, following the options survey and discussion on the 2026-07-07 tomography call (notes). Live options: a data-vector shift (potentially via DES's Smokescreen) vs. an automated repeat of the previous n(z)-shift approach. Sub-issues track the concrete work; decision to be continued, including at the Paris in-person meeting.