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/compare_learned.csv

@@ -0,0 +1,2 @@
+scheme,legit_ser,eve_out,eve_in,jam0_ser
+proposed_learned,0.06358416667,0.9998083333,0.9999833333,0.4046066667