[Client] Add [AppColors] application palette roles

The home-tab buttons' gradient over the static theme background was hardcoded, and accent-derived fallbacks could not be themed or edited: QPalette's role set is closed, so any application-specific color has to live in Cockatrice's own palette layer.

- Add an AppColor::Role enum (AccentStrong / AccentSoft) stored on PaletteConfig and round-tripped from palette-<scheme>.toml under a new [AppColors] section.
- Cache the applied app colors in ThemeManager and expose appColor(Role) with a palette-accent-derived fallback; emit paletteChanged() from applyStyleAndPalette so previews, scheme switches and OS dark mode repaint palette-driven widgets.
- Fill both app roles in PaletteGenerator::fromAccent and surface them as a dedicated section in the palette editor.
- Drive the home-tab buttons from appColor() whenever the background source is the theme (any theme, not just built-ins).
- Ship AccentStrong / AccentSoft values in the Fusion and Default default palettes so the static home-tab buttons keep their classic greens.

# Conflicts:
#	cockatrice/src/interface/widgets/general/home_widget.cpp

cockatrice/src/interface/widgets/general/home_widget.cpp

@@ -61,6 +61,7 @@ HomeWidget::HomeWidget(QWidget *parent, TabSupervisor *_tabSupervisor)
     // Scheme flips (light/dark/system with an OS switch) fire on themeManager,
     // not on SettingsCache::themeChanged, so re-resolve the variant background.
     connect(themeManager, &ThemeManager::themeChanged, this, &HomeWidget::initializeBackgroundFromSource);
+    connect(themeManager, &ThemeManager::paletteChanged, this, &HomeWidget::updateButtonsToBackgroundColor);
     connect(&SettingsCache::instance().appearance(), &AppearanceSettings::homeTabButtonColorChanged, this,
             &HomeWidget::updateButtonsToBackgroundColor);
 }
@@ -105,23 +106,27 @@ void HomeWidget::loadBackgroundSourceDeck()
     backgroundSourceDeck = deckOpt.has_value() ? deckOpt.value().deckList : DeckList();
 }
 
-static bool isDefaultBackgroundAndTheme()
+static bool usesThemeBackground()
 {
     QString sourceId = SettingsCache::instance().appearance().getHomeTabBackgroundSource();
-    return themeManager->isBuiltInTheme() && BackgroundSources::fromId(sourceId) == BackgroundSources::Theme;
+    return BackgroundSources::fromId(sourceId) == BackgroundSources::Theme;
+}
+
+static QPair<QColor, QColor> paletteDerivedButtonColors()
+{
+    return {themeManager->appColor(AppColor::AccentStrong), themeManager->appColor(AppColor::AccentSoft)};
 }
 
 QPair<QColor, QColor> HomeWidget::determineButtonColor() const
 {
-    static QPair defaultColor = {QColor::fromRgb(20, 140, 60), QColor::fromRgb(120, 200, 80)};
-
     auto colorSource =
         HomeTabButtonColor::intToSource(SettingsCache::instance().appearance().getHomeTabButtonColorSourceIndex());
 
     switch (colorSource) {
         case HomeTabButtonColor::Automatic: {
-            if (isDefaultBackgroundAndTheme()) {
-                return defaultColor;
+            if (usesThemeBackground()) {
+                // Static theme background: follow the theme's accent colors.
+                return paletteDerivedButtonColors();
             } else {
                 return extractDominantColors(background);
             }
@@ -130,7 +135,7 @@ QPair<QColor, QColor> HomeWidget::determineButtonColor() const
             return extractDominantColors(background);
     }
 
-    return defaultColor;
+    return paletteDerivedButtonColors();
 }
 
 void HomeWidget::setRandomCard(ExactCard &newCard)