fix(matlab): rate y-grid every 0.02 (was auto-subdividing to ~0.01)

MATLAB's minor grid ignored MinorTickValues and auto-subdivided finer than
0.02. Make 0.02 the actual (major) tick spacing for rate, label only every 0.1,
and let grid on draw the fine 0.02 gridlines deterministically. Regenerated all
figures.

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

analysis/matlab/variation_plot.m

@@ -54,12 +54,20 @@ if strcmp(metric, 'count')       % count: tick every 5, but label only every 10
         if mod(yt(k), 10) == 0; lbl{k} = num2str(yt(k)); else; lbl{k} = ''; end
     end
     set(gca, 'YTick', yt, 'YTickLabel', lbl);
-else                             % rate: fine minor tick marks every 0.02 (no labels)
+else                             % rate: tick every 0.02, label only every 0.1
     yl = ylim(gca);
-    set(gca, 'YMinorTick', 'on');
-    ax = gca; ax.YAxis.MinorTickValues = 0 : 0.02 : ceil(yl(2) / 0.02) * 0.02;
+    yt = 0 : 0.02 : ceil(yl(2) / 0.02) * 0.02;
+    lbl = cell(1, numel(yt));
+    for k = 1:numel(yt)
+        if abs(yt(k) / 0.1 - round(yt(k) / 0.1)) < 1e-9   % multiple of 0.1
+            lbl{k} = num2str(round(yt(k), 1));
+        else
+            lbl{k} = '';
         end
-grid on
+    end
+    set(gca, 'YTick', yt, 'YTickLabel', lbl);
+end
+grid on                          % gridlines fall on the ticks (rate: every 0.02)
 % Add breathing room between the y-axis label and the tick numbers.
 set(ylh, 'Units', 'normalized');
 yp = get(ylh, 'Position');