feat(matlab): phased days x tDCS LME + Monte-Carlo power analysis

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>

analysis/matlab/run_power.m

@@ -0,0 +1,8 @@
+%RUN_POWER Monte-Carlo power analysis for the early-phase days x tDCS interaction.
+%   Usage: matlab -batch "run_power"
+%   Uses the fitted mergeA2 early-phase (0-5) LME as ground truth and reports
+%   power (cluster-honest per-animal test and the LME test) across a range of
+%   subjects-per-group, at the observed and half-observed interaction sizes.
+%   See tdcs_power_sim for parameters.
+
+tdcs_power_sim('mergeA2', [0 5]);