[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.

oracle/src/oracleimporter.cpp

@@ -110,7 +110,7 @@ bool OracleImporter::readSetsFromByteArray(QByteArray data)
  * A lower index means a higher priority.
  */
 static const QStringList MAIN_CARD_TYPE_PRIORITY = {"Planeswalker", "Creature", "Land",       "Sorcery",
-                                                     "Instant",      "Artifact", "Enchantment"};
+                                                    "Instant",      "Artifact", "Enchantment"};
 
 /**
  * Returns the priority (index) of the given main card type. Known types map to their