Adds tdcs_phase_lme (same LME refit within learning phases 0-5/6-10/6-13, with
per-phase slopes + interaction 95% CI) as phase_* switch cases, and
tdcs_power_sim (Monte-Carlo power for the early-phase interaction, scored by the
cluster-honest per-animal test and the LME test) + run_power. Findings: the
Box-B2 faster-acquisition signal is in the early phase; at n=3-5/group honest
power is 0.3-0.7 even at the observed effect (need ~8/group if effect is as
observed, ~20/group if half). Adds tPhasePower tests. Suite 35/35.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>