Companion to #143 which fixed the frontend to use Claude Opus 4.6 as
the sole baseline. This migration recomputes existing Supabase rows
using the exact closed-form: new = T/3.8M + 10*old/19, derived from
the original triple-provider formula.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
