[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/palette_editor/palette_generator.cpp

@@ -150,6 +150,17 @@ PaletteConfig fromAccent(const QColor &accent, int intensity, const QString &sch
     cfg.colors[CG::Disabled][CR::HighlightedText] = disText;
     cfg.colors[CG::Inactive][CR::HighlightedText] = dark ? Qt::white : Qt::black;
 
+    // Accent: same primary hue as Highlight, so palettes derived from a
+    // QuickSetup accent always carry a matching Accent role.
+#if QT_VERSION >= QT_VERSION_CHECK(6, 6, 0)
+    set3(CR::Accent, hl, disText, hl);
+#endif
+
+    // Application role colors: Strong tracks the primary accent, while Soft is
+    // the lightened, desaturated companion used for button-gradient highlights.
+    cfg.appColors[AppColor::AccentStrong] = hl;
+    cfg.appColors[AppColor::AccentSoft] = hsl(accent.lightness() + 60, qRound(accent.hslSaturation() * 70 / 100.0));
+
     // BrightText
     QColor bright;
     if (achromatic) {