Middle-button pan, persistent tool settings, Auto Select's foreground rule, the new icon (12.6b)

src/Document/ToolDefaults.h

@@ -0,0 +1,11 @@
+#pragma once
+#include <QString>
+
+// Swift's ToolDefaults: toggles kept for the person, across launches.
+namespace ToolDefaults {
+// The app turns them on; tests keep the compiled defaults.
+void enable();
+// The stored toggle, else the fallback.
+bool boolean(const QString &key, bool fallback);
+void set(bool value, const QString &key);
+}