Fix incorrect toolbar color on Qt 6.9+

Fixes #1685

app/main.cpp

@@ -744,6 +744,12 @@ int main(int argc, char *argv[])
     if (!qEnvironmentVariableIsSet("QT_QUICK_CONTROLS_MATERIAL_VARIANT")) {
         qputenv("QT_QUICK_CONTROLS_MATERIAL_VARIANT", "Dense");
     }
+    if (!qEnvironmentVariableIsSet("QT_QUICK_CONTROLS_MATERIAL_PRIMARY")) {
+        // Qt 6.9 began to use a different shade of Material.Indigo when we use a dark theme
+        // (which is all the time). The new color looks washed out, so manually specify the
+        // old primary color unless the user overrides it themselves.
+        qputenv("QT_QUICK_CONTROLS_MATERIAL_PRIMARY", "#3F51B5");
+    }
 
     QQmlApplicationEngine engine;
     QString initialView;