handle window focus (dont run fade and read while not focused)

src/main_screen.hpp

@@ -112,6 +112,7 @@ struct MainScreen final : public Screen {
 	bool _show_tool_id_stack {false};
 	bool _show_tool_demo {false};
 
+	bool _window_focused {true};
 	bool _window_hidden {false};
 	uint64_t _window_hidden_ts {0};
 	float _time_since_event {0.f};