Learned-key stages, per-scheme plot styles, KM naming

exp_learned.py mirrors every structured result stage for the learned key
family at the same SNRs, frame counts and seeds, so Figs. 2, 3, 4 and 7
and Tables IV and VI can carry both realizations of keyed masking.

replot_security.py gains a style registry: colour identifies the scheme
and line style the role, so a curve learned in one figure reads the same
in the next. Previously OMA was grey in two figures and teal in a third,
and blue meant the eavesdropper in one figure and the permutation key in
another.

data/refresh_learned.csv

@@ -0,0 +1,9 @@
+block,legit_ser,eve_ser
+0,0.06381666667,0.9999375
+1,0.06395583333,0.9981941667
+2,0.06397833333,0.999985
+3,0.06386833333,0.9983758333
+4,0.06338666667,0.9999908333
+5,0.06366416667,0.9999133333
+6,0.06398416667,0.9999433333
+7,0.06390583333,0.9809091667