[Icons] Author icon emphasis colors as palette roles

The emphasis levels were computed from the accent at paint time, so a
theme could not vary them: every theme got the same derived strong and
soft tones, and a semantic hue was pushed toward the accent whether the
author wanted that or not.

Give each family three authored roles instead. Icon/IconStrong/IconSoft
carry the neutral glyph ink and Positive/Negative gain the same Strong
and Soft companions. Emphasis becomes a lookup inside the family, and a
caller that names a variant pins that level at every emphasis. The paint
path returns the authored color verbatim; only the filled treatments keep
their saturation floor, because carrying a disc or a fill is a treatment
decision.

Shipped palettes author the full ladder for both schemes; the palette
editor exposes the new rows and the generator writes them. System keeps
deriving its neutral ink from the platform palette, since it ships no
palette of its own.

cockatrice/themes/Plasma/palette-default-dark.toml

@@ -71,6 +71,13 @@ Accent               = #6a4df0
 [AppColors]
 AccentStrong         = #5b3ee0
 AccentSoft           = #a28bf7
+Icon                 = #927fea
+IconStrong           = #b7aaf1
+IconSoft             = #736b97
 Positive             = #6dd58c
+PositiveStrong       = #99e2ae
+PositiveSoft         = #517a63
 Negative             = #ff8a80
+NegativeStrong       = #ffada6
+NegativeSoft         = #926567
 

cockatrice/themes/Plasma/palette-default-light.toml

@@ -71,6 +71,13 @@ Accent               = #5a3ee2
 [AppColors]
 AccentStrong         = #5b3ee0
 AccentSoft           = #a28bf7
+Icon                 = #5439d0
+IconStrong           = #39278e
+IconSoft             = #7569a4
 Positive             = #1b7f3b
+PositiveStrong       = #0e431f
+PositiveSoft         = #5c776d
 Negative             = #b3261e
+NegativeStrong       = #711913
+NegativeSoft         = #95646d