feat(matlab): mergeNaive grouping (control=A2+Naive, tDCS=B2+Right) + GLM/power

Adds cfg.mergeNaive and scenario/paper/phase/power support. This pooled grouping
is the closest replication of the paper's full pattern: paper LME interaction
F(1)=7.30, p=0.008 (paper 7.12/0.008), stim main n.s. (p=0.21 = equal on Day 1),
strong day effect; the overall tDCS advantage is significant at the cluster-honest
per-animal level (rate p=0.003) and well powered. Adds a grouping test. Suite 38/38.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

analysis/matlab/tdcs_config.m

@@ -54,4 +54,11 @@ cfg.mergeB2 = containers.Map( ...
     {'Electrode-Box-A', 'Right-Electrode'}, ...
     {'Electrode-Box-B2', 'Electrode-Box-B2'});
 
+% mergeNaive: pool Naive into the Box-A2 (control) side and Right-Electrode
+% into the Box-B2 (tDCS) side. Control = Box-A2 + Naive (n=7), tDCS = Box-B2 +
+% Right-Electrode (n=4); Electrode-Box-A is left unchanged.
+cfg.mergeNaive = containers.Map( ...
+    {'Naive', 'Right-Electrode'}, ...
+    {'Electrode-Box-A2', 'Electrode-Box-B2'});
+
 end