fix: add braces around switch-case blocks with initialized declarations

MSVC rejects declarations with initializers directly under a case label
(C2360/C2361: initialization skipped by case/default labels), while
GCC/Clang accept them. Wrap the declaring case bodies in braces.

app/graphicsscene.cpp

@@ -35,15 +35,17 @@ static const QColor& ColorSchemaToTextForeground(Qt::ColorScheme colorScheme) {
 #endif // defined(Q_OS_WIN)
 
     switch (colorScheme) {
-    case Qt::ColorScheme::Dark:
+    case Qt::ColorScheme::Dark: {
         static QColor WHITE = QColor("White");
         return WHITE;
+    }
     case Qt::ColorScheme::Light:
     case Qt::ColorScheme::Unknown:
-    default:
+    default: {
         static QColor BLACK = QColor("Black");
         return BLACK;
     }
+    }
 }
 
 class PGraphicsPixmapItem : public QGraphicsPixmapItem