[Icons] Keep semantic red and green on themed glyphs

The one-glyph cutover recolored every icon from a single palette role, so a
disabled deck, a not-ready player and a remove button all lost the red or green
that carried their meaning.

Add Positive and Negative application colors beside the accents, ship
scheme-appropriate defaults for every theme, and resolve them through
ThemeManager. Icons now take an IconTint: a palette role for structural glyphs,
or a semantic role for states and add/remove actions. A disabled semantic icon
falls back to the disabled foreground; on a selected row a semantic tint keeps
its color only while it stays legible on the highlight, and a palette tint keeps
the existing WindowText -> HighlightedText swap.

cockatrice/src/interface/theme_config.h

@@ -20,6 +20,8 @@ enum Role
 {
     AccentStrong,
     AccentSoft,
+    Positive,
+    Negative,
 };
 Q_ENUM_NS(Role)
 } // namespace AppColor
@@ -41,6 +43,16 @@ enum Role
 Q_ENUM_NS(Role)
 } // namespace AppFont
 
+/**
+ * @brief Fallback for an application color role when the active theme does not
+ *        define one.
+ *
+ * Accent roles return an invalid QColor because ThemeManager derives them from
+ * the palette highlight. Semantic roles return an opaque, scheme-appropriate
+ * default so a theme written before the role existed still renders it sensibly.
+ */
+QColor defaultAppColor(AppColor::Role role, bool dark);
+
 struct ThemeConfig
 {
     QString colorScheme;