analysis(matlab): add log(day) model + Cohen's f + power to every variation

Add variation_logpower.m (self-contained) + make_variation_logpower.m,
dropping logpowersim.m + logpower_result.txt into all 28 variation folders.
Matches the paper's power code: models behavior ~ stim + log(day) +
stim:log(day) + (1|rat) (log(day+1), since our day 0 = paper Day 1), reports
Cohen's f (partial eta^2 of the interaction) and the interaction under
residual/Satterthwaite/honest random-slope DF, then runs the Monte-Carlo power
sim on the log-day ground truth (per-animal cluster-honest + LME power).

Notable: under log(day) the accumulating divergence is captured more sharply,
so several full-window scenarios reach honest significance that were n.s. under
raw day (e.g. right_only_d0_13 honest p=0.003, unmerge_d0_13 0.021,
unmerge_d0_10 0.036); Cohen's f is small-medium (~0.10-0.34).

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

analysis/matlab/variations/unmerge_d6_13/logpower_result.txt

@@ -0,0 +1,36 @@
+==============================================================================
+LOG-DAY MODEL + COHEN'S f + POWER -- unmerge_d6_13
+==============================================================================
+model: behavior ~ stim + log(day) + stim:log(day) + (1|rat)   (success COUNT)
+log(day) uses 1-indexed training day (our day 0 = paper "Day 1")
+observed groups: stim n=3, control n=2   nrep=120, alpha=0.05
+
+--- fitted on real data ---
+stim x log(day) interaction: F(1,30)=3.007  p(resid)=0.09315  p(Satt)=0.0931 (df=30)
+  honest per-animal random slope (log-day): F(1,12.8)=2.47  p=0.1406
+Cohen's f (interaction, partial eta^2=0.025) = 0.161  (small-medium; f: .10 small, .25 medium, .40 large)
+
+--- power simulation (log-day ground truth: stim:logday=+22.97, ratSD=7.14, resSD=7.81) ---
+
+ true stim:log(day) = +22.97 (100% of observed)
+  N/group  | per-animal power | LME power
+  ------------------------------------------
+  3        |  0.47            |  0.64  <- observed
+  5        |  0.79            |  0.90
+  8        |  0.96            |  0.99
+  12       |  0.99            |  1.00
+  16       |  1.00            |  1.00
+  24       |  1.00            |  1.00
+
+ true stim:log(day) = +11.49 (50% of observed)
+  N/group  | per-animal power | LME power
+  ------------------------------------------
+  3        |  0.12            |  0.22  <- observed
+  5        |  0.26            |  0.36
+  8        |  0.41            |  0.47
+  12       |  0.53            |  0.58
+  16       |  0.71            |  0.74
+  24       |  0.90            |  0.93
+
+Read the per-animal column as the honest power; the LME column matches the
+paper's power code (anova interaction p, observation-level DF) and is optimistic.