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_summary.csv

@@ -2,3 +2,4 @@ scheme,legit,eve,entropy_bits
 None (fixed key),0.05300666667,0.9997075,23.76910417
 Fresh orthogonal keys,0.1215548611,0.9996535069,23.76910417
 Invariant,0.05304121528,0.9995528819,364.5801064
+"Invariant, learned keys",0.063800,0.997200,364.5801064